360 Cylinder Pressures

Hi All

I have a question (and I think I know the answers) but I would appreciate your opinions.
My 73 Duster 360 has a few issues I want to deal with.
1) It refuses to spin the wheels
2) Its averaging 14mpg
3) It seems to be breathing a little heavy
other than that it runs perfectly.

I know little about the motor.
It has a lumpy Comp Cam (unknown)
Edelbrock Performer Intake
Edelbrock Carb
TTI Headers
Torque Converter unknown
727 Trans
3.23 Gears

It comes on hard around 2500 rpm once moving.

We did a compression test and found 2 cylinders at 75 psi and the rest in the 80's with the 3 highest being 87 psi.
My first thoughts then is that the engine needs replacing or rebuilding.
I understand the high lift cam and low compression will rob cylinder pressure, but how much?
Could it just be that the cam is not right for the engine?

I am temped to throw a standard cam in and see.
Any thoughts greatly appreciated.
Thanks
Kev