I have a 98 Camaro, 3.8L. Recently I have had a new Borla exhaust put on,
new plugs and wires, an oxygen sensor and a mass sensor and some other
odds and ends to fix the code that diagnostics picked up...

I have a new problem...

The car starts fine, but as I accelerate the car jerks and the RPM's
bounce slightly then smooths out. This only happens in 1st, 2nd and 3rd
gear. Once I get the speed above 40 and into 4th or 5th gear it is smooth.

When it idles, it is a bit rough and the air pressure gage which is
usually at 60 drops down to 30.

I'd appreciate any advice from anyone.

Thank You very much! :)