My 4L60E (in a '97 C1500, 5.7L...rebuilt 50,000 miles ago) has recently started hesitating going into drive. It goes into reverse with no problems, but when shifting to drive, it takes about 4 seconds to finally get there...sometimes requiring a quick little blip of the throttle.

What's the deal? Shifting solenoid? Something worse?

Wes;
Have you done a fluid and filter change since the rebuild? Is the fluid level low? I'd suggest the fluid and filter change which will require dropping the pan allowing inspection for shavings/particles some grey graphite like material on the magnets is normal, larger chunks are not.

No, I haven't done a change...probably should have...but the fluid level is normal. I'll do the change and try that first. Thanks for the advice!