'97 z71

I have a '97 z71 that has 145000 miles. I can be driving it and get up to about 45 mph in OD and it will start skipping and cutting out bad.I will pull it down in 3 and it runs just fine.It only does this in OD.What might this be.Thanks for any help that any of ya"ll can give.I have been driving this truck since '99 and my payment book only has 2 pages left on it.The front and the back and I don't want another one.Thanks

Has it ever been tuned up?
How is fuel pressure?
Any check engine lights/codes?

are you kidding me? you still have a payment on a truck you have had 10 years? Wow, your bank is one in a million, anyway, on topic.

If you lay into the pedal does it get worse, or stay the same. If you down shift and lay the pedal down does it not do it?

I think he meant the front and back cover. Has the trans fluid and filter been changed, dont backflush the thing. When in OD will slightly pressing the brake (to engage the lights but not the brakes) will the surging stop?