My mate (who has nothing to gain from the shop), said that a mechanic whose asked to tune an engine (regardless or before or after an exhaust swap) will check for leaks that are basically impossible for a non-mechanic to find.. and check the ignition timing and check the fuel mixture ratio.. and he said a few other things too. These all sound kinda useful to have checked at least one in a blue moon... surely? And if i'm getting work done anyway, what better time?

I can tell the mechanic the parts I've swapped out or recently installed, and direct him not to futz with them, just to do the other stuff, right?
I reckon that kinda stuff sounds worth maybe 60 bucks at most though.

The muffler place is gonna check my cat for free, pretty kool Cos i'm suspicious of it (it was replaced about a year ago and is starting to act the same. These replacement parts and other work are to eliminate any simple causes, and the exhaust just for the heck of it).