426 cat stops moveing

i have a 1987 2wd 426 cat wit 2400 hours on it. it has developed a problem, about 5 months ago i was digging stumps and i went to reposition and the machine wouldn't move fwd or rev. i took the floor pans up and tapped on the neutralizer selonoid and then it worked. i have put about 200 hours on it since then. i drove down to the neighbors house 3miles away and loaded rocks into my dump truck for 8 hours. then on fri roaded the backhoe home. today i started it to start doing the latest project and it did it again. i shut it down and tapped on the neutralizer sel. nothieng. fluid level is good and the trans filter was replace about a year ago. i can hear the selonoid click when i push the button on the shifter and on the loader bucket so i would thing it was working. i shut it off and came back in about 2 min and it moved about 80' then just stopped moveing again. let it sit a couple min and started it and it worked. put it in rev and drove back to the garage . and when i put it in neutral then fwd it was dead again. sounds reminiscent of this thread http://ift.tt/1WU7Fwf; but with only 2400 hours i would be surprised if it had a bad transmission. any advice is welcome i am not sure where to start.

426 cat stops moveing