Poor mileage on Chevy 350?

I recently replaced the passenger side head gasket on my 1985 GMC 1500 with the 350 and it doesn't run like it should. I know I did the job right and everything is torqued down to the specs in the Haynes manual. Before I did the job, it would get about 10-15 mpg with a hesitation at take off and it was burning coolant and trading compression between two cylinders. After the job, the hesitation is much worse, and the mileage appears to be about 1-2 mpg, but it does idle much better and is much better once at speed and still starts up as easily as before. I thought that maybe it had something to do with me leaning out the carburetor a bit, even though I wouldn't think that would do this, and it's still the same. It does appear to get worse as it warms up. The engine is about 3 years old with maybe 10,000 miles on it; carburetor, intake, fuel pump, distributor, and valve covers were taken from previous engine and they were new on it because that was a replacement engine, so those things are about 10 years old. Distributor has had a new coil, cap, rotor, control module, plug wires and plugs and the engine got an oil change after I did the head gasket. Really the only thing I appear to have solved was the coolant burning, compression trading, and run on with the engine. I checked for puddles of gas and couldn't find any signs of leaking, but I could smell gas all through the house when I never did before. Any ideas as to why the mileage is so incredibly poor and why on take off it has to decide if it wants to go? Thank you for any and all help.