engine missing slightly at ~2000 rpm

tried to search the member archives but no hits. lateley i have noticed a slight miss at just above 2k rpm. and sometimes at idle just after starting it tries to rev up and makes the auto tranny want to engage. 4 litre, flow master, turbo city open element filter. 91 limited. changed the cap/plugs/ and going to put in new wires tomorrow. my two questions are , possible vac leak? and i think i may have recracked my exhaust manifold slightly. will the exhaust cause this skip at freeway speeds. it is running ok but suddenly seems like it is just not quite as strong as it used to feel. any likely places to look?

compression test...... I don't want to scare you but i had similar issues and it was a burnt valve....

CPS

If you haven't changed the Crankshaft Position sensor (engine speed sensor) you are overdue and should change it. It will cause a light load miss at 1800 - 2000 RPM

thanks, the engine has about 30k on in but will check the compression . my guess is that the guy i bought it from didn't change the position sensor though and that would have about 225k on it. just an odd note, would a cat convertor
affect it too? do they usually break apart or plug? need and excuse for a high flow....