Old 1981 Allegro motorhome with AT545 well maintained I purchased to horse camp in. Drove 45miles to camp early last summer, stopped on the rode to survey camp, and vehicle lurched and jumped and shuttered even in neutral. Tried to move it ahead and it lurched and stalled the engine (3208 Cat) several times. Called and talked to my mechanic buddy and he asked what it did in reverse when i shifted it to reverse it snapped the pinion shaft in two. I found another diff. and installed it with the same results. lurched jumped and stalled in forward gear and (should have never done this) broke the pinion shaft in the diff. when shifted to reverse. These diffs are $800 from the bone yard. Is this a locked up torque converter? Any transmission tests that can be done on the AT545. Could the trans itself bust the pinion shaft? Any help would be appreciated.