1994 Roadmaster Estate Wagon Idling high while stopped

I have a 94 wagon and have been having problems for months now with the engine seeming to misfire while climbing hills or just traveling at 50 mph. I have changed spark plugs, wires, distributor (along with water pump), cooling water sensor and the problem has gotten worse, now the engine racing while stopped or idling. It runs great at 75 mph but i think the problem is affecting my gas mileage, too. I have , 5.7 L engine, auto trans, 125,000 miles. My mechanic buddy put it on the computer and it said i had a bad injector and that was also changed. Any ideas? Help!!

Have you checked coil output?

Check for a vac leak?

Check for codes?