With my new parts for the 3.4 swap , I made sure to get the parts from a 90 trooper for the starter and flexplate applications.As for flexplate and flywheel , they are basicaly the same , the flywheel is for manual trans and the flexplate is for auto , although some places call both a flywheel.
Something is definately wrong if its grinding teeth off right away , like the teeth aren't matching up properly , whether the starter is off , or the flexplate teeth aren't in sync.Did you get a flywheel for a trooper when you put your truck back together?Or did you use the 3.4 one?My engine didn't come with one , so I can't tell you for sure if the teeth would match up or not , I just went out and bought brand new for 50 bucks.