First of all is the extended cab? 1. If so check to see if there is a 1/2 inch plate in between the center carrier bearing mount and the frame - if not there was a TSB out regarding drive line alignment that has not been done. 2 Possible clutch problems. 3. If the idle is too high it will also shudder in 1st & 2nd. 4 Some "launch shudder" is normal. Hope this helps.
Happy Trails.
Bob