since my 'new' (2nd hand low mileage) engine was installed I have noticed that its popping and crackling from the exhaust more that it used to.

Also in 4th and 5th gear mainly under acceleration its a bit hesitant and generally don't seem to be as smooth as it was before.

having my map tweaked soon, will this cure it?

Alternatively is there any sensors you could think of that could cause these issues.

Idles fine and has no dead spots as such


Advice much appreciated

Mark