I just recently got an 84' m923A1, and after driving for about 15-20 mins. The front hubs will get extremely hot and or smoke. The truck is also limited to around 20 MPH(downhills around 25-28 MPH). Truck has no visible or audible air leaks, so personally I think the front brakes are possibly rusted . Ive also been trying to find a -20 or -30 TM, but nothing but only the -10 pops up on internet searches.