i bought my truck from a friend who used it on his farm it had a rough life till i got a hold of it. Installed a toyota 4:10 rear end and did every thing from long haul trips 110 mph power cruizes down the freeway and even toasted the tires in all gears even reverse, and of all things to cause problems just cruzing around the mall one day after work, one of the gears on the counter shaft let got and showered the rest of the guts of my tranny with all kinds of shapnull

Go to a local auto salvage yard and look for a new tranny. For the cost of buying the replacement parts you could just get a whole different tranny.