if it sounds like its 'missing' you could have a sparking problem, happened in my LS before, check your plugs/plug wires/dist cap/ rotor and make sure all your plugs are still sparking. sometimes just replacing all those things along with a new air filter and fuel filter can make a world of difference.
as for the compression test just look for consistent numbers accross all 4 cylinders.. anywhere from 160-180 would be good numbers as long as they dont vary much. ie - 160-160-160-160 would be alot better than 185-185-130-185.
good luck