02' 4.6is Supercharged / 107k / Trans. Fail. Safe

[740ilDuke]

So, the X5 finally arrived after about a month of back and forth, happily in nice cosmetic shape overall just needing a little paint correction on the nose from stone chips and on the rear bumper. I bought it aware of TFS.

Moving on.

As I've been in an E38 and had a E53 before, Im familiar with the 5hp24, more or less - like anything it needs to be serviced.

The Issue: Once warm it slips in 1 and 2 and slams into gear. So, Im torn between a transmission flush which would clear the cooler of debris if it's clogged and just swapping transmissions. I found one locally for $800 the seller says was rebuilt 15k miles ago. No paper work, but gave me his number to call and discuss. The other is $1350 shipped from CA with 70k miles. I think I can get the swap done for $300 labor. Leaving me with the fluid / filter / gasket and potentially going ahead and sourcing the 4.6is rebuilt torque converter, or just moving mine over. But, with 458HP in front of this slush box, a rebuilt unit is probably the smart move.

A friend with the same truck just swapped his gearbox for similar reasons. The 4.4 X5 box will work without issue, the only differences being the TC and Valve body. He has not noticed any difference in performance or pulling a trailer and left the valve body intact, and only swapped over his TC.

That said - should I just aim towards one of the above boxes, or have a legitmate flush done.

Thanks everyone!