Few questions, I need help with.
 

first off My car is a 1999 z-28 ls1 automatic.
My questions are:
EXHAUST:
Where can I find a muffler delete pipe? (or open exhaust kit) I seen one on ebay awile back and I can no longer find it.
I have SLP long tube headers and the slp Y-pipe, the owner before me gutted the high flow cats, for some crazy reason, I got the car with no rear exhaust, it had SLP loudmouth exhaust on it. but it was a repo and they stole it (along with the wheels, groundeffects and a few little things) I took it to an exhaust shop and had them put a flowmaster on it and it now sounds like S**t..... the muffler is super quiet, the car sounds like a V6 with a flowmaster... Anyone know why it is so quiet? I have a 94 firehawk lt-4 , with BBK shorties, No cats and a flowmaster and it sounds perfect, very loud. I was thinking that with the SLP longtubes the LS1 would have sounded loud. not quiet and out of tone.
So Im looking for a muffler delete pipe.
More questions:
TRANSMISSION: My transmission shifts good for the most part, but every now and then it will slip, but only in overdrive. If im running about 60-65mph and let off the throttle and then back on it will slip, but if i drop it a gear and put it back in overdrive it wont slip anymore. also any speed over 70mph it wont ever slip, no matter what i do to it.
Any ideas?
ECM: Someone has deleted the EGR , and cut the wires for the O2 censors, made a real mess of everything; Im wanting to reprogram the ECM to just "delete" the EGR and O2 sensors. Ive been looking at a few programers online like tunercats and HPtuners. HPtuners I like but I Hate the fact that it is $500+ and only works on one type of car.
the tunercat program looks good, it will work with both my Lt4 and my Ls1. But I can not seem to find much info on it. Has anyone ever used it? and what do you think? Or other programers do you recamend?
MOTOR: Does the ls-6 intake add power to the ls1? Ive read online that the 2000+ ls1 camaros use the ls6 intake and have a higher lift cam to work sim to the EGR? Since I don't have an egr anyway, would an Ls6 intake flow any better then the stock ls1?
FUTURE MODS..... Im wanting to drop the 4l60e and repleace it with a t56, I know that the 93-97 t56 are temec and the 98+ are made in mexico borg warners. Ive read that the temec are a better built transmission? are the bellhousing bolt pattern the same? Im not to up on the genIII aluminum small block. And will I need to replace the ECM if I switch over to a t56?
BODY: where can I find a factory groundeffects package? this car had one from factory and ive seen a few others that do, but I can not seem to find anyone that makes OEM looking kits, I don't want a "transformers" looking kit.
A used kit would be perfect, anyone know of a camaro junkyard that would have the ground effect package?

thanks!

The Ls6 intake can give you a boost, maybe 10-15 hp. Cam shouldn't be a factor. 98-00 cams were all the same lift .500/.500 with 119.5 lsa.I was able to delete my rear o2s with the DiabloII.It may also delete AIR and EGR . You should finish the slp headers and ypipe with the loud mouth system. You won't be satified with bits and pieces.