I don't think my left rear brake is working.
 

Got the first slick day today since I've had the 2001 4.4. Noticed that whenever I tried to stop the nose would always go to the right. Pretty scary. When we got home, I had my wife stand on the porch and watch the wheels as I tried to stop. Every wheel except for the rear left would be locked.

My DSC, ABS, and Brake lights have been yellow for a while. The speedo stopped working the other day but started again and has worked since then.

Easiest way to diagnose would be to have the truck in the air on a lift while having someone hold pressure on the brakes. Then start cracking the line loose in different connections, starting from the wheel, until you find where the pressure starts/stops. Then you could see if there is a damaged hose blocking pressure etc. If thee is no pressure anywhere, it might be airlocked in the DSC module, maybe a pressurized system bleed by the dealer while they activate the bleed function of the DSC via GT1 could get it working.

Either way it goes, it may be worth the 1 hour diagnostic fee to have it properly diagnosed by the dealer.

Your vehicle sounds like it may be a danger to other drivers on the road. You don't have ABS, DSC, properly functioning brakes, and only an occasional speedometer? Anything else not working?

Recommend you find a mechanic to give it a good look over, before someone gets hurt.