My 2001 4.4i S/P has the Dinan throttle body, engine and transmission software which gives the engine about 300 hp and 350 lb/ft of torque. The transmission is the 5 speed Steptronic. It does not have "Trailer Stability Control" (TSB) as that functionality wasn't available until about 2003, BUT it is my understanding that TSB does not have anything to do with the transmission while towing. It only kicks in when the sensors detect a "sway" condition (tail wagging the dog) upon which it will de-throttle the engine and apply the X5 brakes in an effort to counteract/correct the "sway".

The “Dynamic Stability Control” (DSC) on my 2001 X5 should also kick in if my tail starts wagging my dog, so I would guess that the TSB is either DSC by another name or a more sensitized DSC since the X5 has no OEM trailer brake interface to independently apply the trailer brakes to straighten out a “sway” condition.

The 5 speed Steptronic locks-up the torque converter clutch (goes into direct drive as per a manual transmission) at an “indicated” 62 mph (about 58 gps mph) and un-locks the torque converter clutch at an “indicated” 60 mph (about 56 gps mph). The 6 speed probably has different lock-up parameters which would need to be explored. That being said I tow in MANUAL MODE as follows when accessing an Interstate Highway:

In MANUAL MODE 1st ALWAYS start off VERY SLOWLY with partial throttle since the drive train needs to be turning to provide “hydrodynamic” lubrication (see my post “Lubrication 101” @ http://www.xoutpost.com/articles.php?...cle&artid=208).

If not on a grade, shift to 2nd at about 2,500 rpm (I back off the throttle just like you would do on a manual transmission to allow the shift without engine torque), then you can “floor” the throttle WITHOUT DEPRESSING THE KICKDOWN BUTTON at the bottom of the throttle travel if you wish.

If not on a grade, shift to 3rd at about 3,000 rpm (back off the throttle, etc.), again you can “floor” the throttle. IF YOU ARE ON A CONSIDERABLE GRADE, hold the throttle down until the tachometer hits about 4,500 rpm (indicated 62 mph) when you will see it drop about 700 rpm as the torque converter clutch locks-up putting the transmission in “direct drive”. As the torque converter clutch locks-up I always IMMEDIATELY back off the throttle to allow it to do so without engine torque (the lock-up occurs much more quickly with much less slip). Then go to the floor with the throttle to continue accelerating.

If not on a grade, shift to 4th at about 3,000 rpm, etc. etc.

If not on a grade, shift to 5th at about 2,200 rpm (62 mph). You’ll see the tachometer start to drop (back off the throttle) as the transmission locks-up the torque converter. Go to the floor with the throttle and accelerate to an indicated 70 mph (about 2,600 rpm). ENGAGE THE CRUISE CONTROL and set it at 70 mph (gps 66 mph). LEAVE THE TRANSMISSION IN MANUAL MODE!

The cruise control is far more sensitive in maintaining speed and it’s mind doesn’t wander. The cruise control, with the transmission in MANUAL MODE, will max throttle the engine WITHOUT “KICKING DOWN” THE TRANSMISSION. I use 70 mph indicated because it gives me a 10 mph locked-up torque converter “zoom” over grades.

THE MAIN POINT TO KEEP IN MIND WHILE TOWING IS TO KEEP THE TRANSMISSION OFF THE TORQUE CONVERTER AND FROM “HUNTING” GEARS IN AN EFFORT TO MAINTAIN A GIVEN SPEED. Hunting gears wears the clutches, heats the clutches and the transmission fluid. Additionally, when the torque converter is UN-LOCKED, the transmission fluid is being heated within the torque converter due to fluid friction. HEAT IS THE ENEMY OF ANY LUBRICANT!

When climbing a grade in 5th gear with cruise control engaged at 70 mph speed will bleed off (throttle at max) right down to an indicated 60 mph and the torque converter will remain locked-up. If the grade is crested the throttle will remain at max until 70 mph is restored.

If the grade is such that the indicated speed drops below 60 mph (about 2,000 rpm) the torque converter will unlock and your rpm will increase to about 2,700. At this point I manually depress the throttle to the floor (don’t depress the kick-down detent) and simultaneously disengage the cruise control. If the grade is such that it is almost crested I leave the transmission in 5th, torque converter un-locked, until the indicated speed reaches 62 mph and the tachometer starts to drop indicating torque converter lock-up at which time is back off the throttle for lock-up, and then press the cruise control resume which max throttles the engine until 70 mph indicated is restored.

You will have to down shift to 4th if it is required to climb a grade (use manual max throttle). If you’re indicated speed reaches 62 mph in 4th the torque converted will lock-up (release throttle for it). After lock-up go to max throttle and engage cruise control (in 4th). Monitor the “Miles per Gallon” gauge to judge engine loading. It will be maxed out at 8 mpg at max throttle until 70 mph indicated is attained, then it will rapidly go 20+ mpg at which time you’ll know the engine torque to the transmission has abated and you can up-shift to 5th WITHOUT DISENGAGING THE CURISE CONTROL.

You’ll find that 4th and 5th gear will handle 95% of grades. I’ve been over the continental divide 3 times and had to use 3rd gear often on the climb but only had to use 2nd about 3 times (it was too low as I could accelerate the grades in it).

When descending a grade or approaching a stop down shift through the gears (“feathering” the throttle) to take advantage of engine compression.

If you are towing any load of consequence (4,000 lbs+) I highly recommend using a 5W-50 or 15W-50 engine oil as the 50 viscosity will protect the engine MUCH BETTER during heavy load, low rpm duty.

Additionally, if you are towing a large rig like mine seriously consider the purchase of the Hensley “Arrow” hitch interface which I use. It completely negates sway without friction devices; no smoke and mirrors. You can find details on it at: http://www.hensleymfg.com/

I’ve told you more than you EVEN WANTED TO KNOW! Hope some of it helps.