Poor Downshift while Decelerating?

[Ininkus]

Newbie here. I've searched the forum but can't quite find a similar problem as mine....

 

I drive around 1000 miles a week. Almost all highway miles. Everything runs smooth except when I get off the highway and decelerate on the offramp. It seems to downshift erratically, or rather - maybe not downshift soon enough. Almost like it stays in high gear too long. And if I press the gas after decelerating, it seems to really get bogged up. About 3 minutes off the highway and all is well again.

 

Any ideas? Just did a tranny service, no major improvement. No transmission overheating codes or anything.

 

Thanks,

Richard

2001 GMC Sierra Z71 ExtCab