The transmission in my work pickup seems to be acting up. If you start it up and take off, it shifts up through the gears just fine but after a few miles of driving, all of the sudden it acts like the transmission is slipping....in all gears. Stop, put it in reverse to turn around and you hear a grinding sound and it won't move. Let it sit for a few minutes, and you can start it up, back it around, and drive it nearly home before it does the same thing again.

Anybody have any clues what might be wrong with this outfit? Transmission oil pump going bad? Pickup is a '97 with 150,000 miles on it.