Tractor Repair: 2590 JI Case, ji case, control valve

Question
I have a 1983 JI Case 2590. Tractor will start then bogs down and dies instantly. Will start in reverse ps but it's still lugs motor down. Any suggestions?

Answer
 If this happened suddenly without prior powershift problems, you have one or more pilot spools stuck in the powershift control valve.  Remove the pilot spools from the control valve and clean them, and polish them if necessary until they slide freely in the bores.