difficult to accelerate or neutral when engine is warm.

Okay my next problem is this, 80 firebird when cold it runs good no problems find. Took it for a 15 min spin around the block and it was becoming a bit more difficult to accelerate. Drove it back home (up hill parking) put it on neutral to allow it to roll back and it was like my foot was on the brake?

The car shifts on all gears, ebrake works good. No transmission leak or funny noise.
The car cooled down, started it, shifted to neutral and it rolled back just find.

Any ideas on what can cause this?
I just installed a new distributor, rebuilt carb, radiator, liquids.

Im thinking its the brake pads when warm they expand but not a 100% sure

thanks