I have a 1988 gmc sierra k1500 single cab short box stepside with a 350 and a 700r4 tran. i replaced the fuel pump the truck started fine. I tried to put out in gear and it started to grind then nothing i can shift from park to 1st and its like all the gears are gone truck will not move. trany fluid is new and full. I'm wondering if any one would know what went out.

Mileage? And this happened right then when you changed fuel pump, or did it drive for a while?

is it up on rack for pump job,maby the driveshaft pulled back to tip of splines

throw out bearing?? and coincidence

It hasn't drove in a year or so we put the trany and transfer case back in to change the transferase but the truck wouldn't start after. I toke the box off to change the fuel pump and now it runs and starts fine. I tried to put it to drive and nothing.

I was thinking it may be the pump within the trany but I'm not sure

Have you made sure tranny fluid is getting to the torque convertor? I am gonna be gone a minute or 120 maybe....LOL I be thinking and I'll be back, it's tough to do this kind of stuff on tv, but we'll see, ok internet. But diagnosing a prob. like this isn't easy, unless you want to lay under the truck with a lap top, not kidding, well maybe. But it beats running back and forth to the house and especially if you can get me sound. no joke?

web cam.....LOL WT heck why not