2001 Chevy 2500HD 8.1L, Allison Trani. That jerks

[Robdam]

I got a 2001 Chevy 2500HD 2wd, Allison train, 168,000 miles on truck . 60,000 miles on Jasper trani., ONLY used to pull a fifth wheel,42 ft being the largest, my Dad bought the truck new, I'm second owner. The problem is , not all the time but more often then I like, when you start the truck it makes a "clunk" noise and jerks forward, hard, or after changing from reverse to drive or drive to reverse it will snatch you. When approaching a stop and it down shifts , when it's shifting to first it dang near stops the truck. Sometimes when not pulling a load it feels as if your puling on a concrete highway with the jerking and then it straightens out.?? Hope all this makes sense and someone can give advice. Thanks

[00Silverado4x4]

I couldn't begin to tell you what it could be but I will suggest that you take it to good trans shop and let them have a look at it.