99 3/4 ton hd suburban OD problem

just bought a 99 commercial grade suburban with jasper crate motor about 40,000 miles on that. trans fluid clean an full, motor runs great, while driving though it seems as though over drive gear only kicks in when i let completely off the gas as i see the rpms drop accordingly. and as soon as i touch the gas again i can feel it shift back to third. all other trans function is great no hard shifting seems smooth as can be. i'm usually a ford guy but the deal was good. any direction as to where to look would be appreciated. i haven't checked for codes yet i'll do that soon.

just bought a 99 commercial grade suburban with jasper crate motor about 40,000 miles on that. trans fluid clean an full, motor runs great, while driving though it seems as though over drive gear only kicks in when i let completely off the gas as i see the rpms drop accordingly. and as soon as i touch the gas again i can feel it shift back to third. all other trans function is great no hard shifting seems smooth as can be. i'm usually a ford guy but the deal was good. any direction as to where to look would be appreciated. i haven't checked for codes yet i'll do that soon.

Best to check for engine running and transmission problems and data and codes with a good engine/transmission capble scanner.

Remember engine has to be running good for the transmission to run good.

Post back any engine or transmisssion codes or out of spec data.

code check shows clean, one thing i failed to mention before was the idle its running 5-600 rpms at idle seems low. and once or twice its cut off when shifting into reverse.

code check shows clean, one thing i failed to mention before was the idle its running 5-600 rpms at idle seems low. and once or twice its cut off when shifting into reverse.
Was Code check done on a transmission/engine capable scanner?
Any history codes?
Did transmission data read out ok?