72 C10 - need more power to wheels

[72TXSuperCheyenne]

Just purchased my first "classic." It is a 1972 C10 Super Cheyenne. Engine is a 350 CI, do not believe anything special in regard to heads, cams, inards etc.

It has a Edelbrock high rise intake. I upgraded to a new Edelbrock 600 with electric choke and put headers with 2 1/2 pipes to flow master mufflers.

It has a THM350 3 speed auto and looks like stock 12", 12 bolt rear end.

The engine runs and sounds GREAT. HOWEVER, instead of acceleration expected of a 250-270HP (?) engine, it accelrated like a YUGO at times.

What should i explore for immediate lower cost fixes? Planning on new drive train, 400HP crate engine, 700R4 tranny, and new rear end next year, so do not want to spend too much.

thanks