Changing mid-pipe and catback: Is a tune needed?

Nope, no tune should be needed for midpipe back exhaust...Might help out for long tubes though since they tend to make the car run more rich...

I might be wrong, but I felt a little drop in low end power, when I put on my mac offroad h pipe. Of course the top end is where these cars make power, and the performance is noticed. It shouldn't mess anything up though. Plan on wakeing the neighbors! And the mils just keep the check engine light off. it is basically just a resistor.

I noticed a drop in the low end power as well when I put on my Flowmaster Super 40 - 2chambers. I also noticed that I had to adjust my driving. I was moving into 4th and 5th at lower rpm's now it wants it into higher rpm's. etc I used to hit into 5th at 65-70 now it doesnt want it until say 80-85+. Is that normal. I also noticed it gets real deep in the sound. Would my gap in the spark plug have anything to do with the power adjustment? Ive got the Autolite platinums AP-764s and when I first got them DUH I gapped them. Ive seen in the forums where you dont want to gap the platinum series plugs. I took them out and regapped to .052 and it helped but it still seems this thing is running rich and not up to power strength.
I did notice that in 3rd and 4th as I hit 4k rpm's the power dumps on big time.
Any help or input.

post-edit: sorry dude didnt mean to steal your thread there

I didn't notice a drop in power from the mufflers, just the mid pipe, without cats, you probably lose some back pressure. You might want to check out the exhaust forum, but I wouldn't expect a drop in power from flowmaster mufflers, unless they are restricting power due to a blower or something like that.