Terex Ta27 trans or hyd pressure surge.

Hello. I’m working on a terex 2004 ta27 haul truck. The issue is the there is a surge it seems in the trans pressure. Every time it it seems to release it the trans temp needle with peg out and then zero out. Also when the body is raised or lowered at an idle the truck will try and stall out. Kinda lost on this one as don’t have much time around terex. Any info is greatly appreciated. Thx