Tranny problem! Slips sometimes other times perfect.

[silver67]

So for about two weeks now, My truck has been having tranny problems. I got in it one day and at about 1900 rpm it would slip until about 3200 rpm when it shifted into 3rd, this kept up for a few days, I took it to a tranny shop and it continued. They told me to take it home take the super chip program out and put it back to stock. So I put it back to stock and it continued to slip going into second. I parked the truck for two days, then I went to drive it to the tranny shop and it shifted perfect, I took it to the shop anyways they put there diagnostic tool on it and everything checked out perfect. Then when I left the tranny shop the O/D off light started flashing, but was still shifting fine. I drove it for a few days after that and this afternoon it started to slip again!
All fluids checked out fine aswell.
Any suggestions?
The shop thinks its a computer problem.
Thanks,
Kyle

[ipz2222]

I didn't see anywhere what your truck is???? 2nd gear is the one that burns out the most.

[silver67]

Oh sorry.
My truck is a 2001 7.3 with 138,000 miles.
Thanks,
Kyle