Sluggish 86 Tbird 5.0 EFI

I have an 86 tbird with a 5.0 fuel injected engine. I just had the engine
rebuilt top to bottom and I installed new injectors, EGR valve and all
the normal tune up items.
It starts good, is timed on the money but it idles unevenly in park or neutral, kind of lopes.
When I put it in gear it levels off and idles fine.
Takes off from a stop like a scared rabbit and will continue to
accellerate fine.
However, if I'm cruising 30-50 mph and accellerate, it is really
sluggish unless I press into passing gear.
Can anyone tell me what is wrong?
Thanks for your time!