Without getting a hold of the previous owner there is no way to tell what type of tuner or who's tuner was used on your truck.
Other than that, you will be stuck in having to purchase a new tuner and overwriting what is already on the ECM.

 

That's what I figured.....any suggestions for a basic tuner that would overwrite current tune without having to go back to dealer to put back to stock? Stock isn't going to work with full delete on truck even for a short ride home I guess

 

EFILive from a reputable source will flash over what is currently in the truck.

 

Common situation with buying any used modified vehicle these days.

Who knows what program is in the ECM. If its an 68RFE auto trans, it could even have unknown trans programming.

It may even be worthwhile getting a fresh stock ECM program from the dealer and start completely clean.

 

Won't that mess with the truck if it's been deleted? Any electronic flash programmer I've ever worked with has to erase the flash chip before it can write new data, it's not like a hard drive, so paying the dealer likely would't have any real effect other than lightening your wallet

 

Flashing a stock ECM program into a deleted truck will set off a ton of codes and the CEL.
However you will be able to drive the truck a short distance if needed.

This will ensure the ECM program is back to a known stock program.
This can eliminate issues when the OP starts the process with a new programming platform.

In the early days of EFI Live, flashing a previously tuned ECM back to stock by the dealer was always recommended.
It doesn't seem to be as much of an issue currently.