My 1995 trans am idles good but back fires under load as soon as I let the clutch out.

I have a 1995 firebird trans am  5.7 lt1.t56 6 speed.  It only has 120k miles and
when I bought it, it ran pretty damn good. But was told it needed the value seals
replace, so i replaced them. When I was unplugging the plug wires, optisprak,
water temp, etc. I mean I marked everything thing I under plugged. Got the
heads of got the seal changed and put it back together EXACTLY the same way
I took it around. But now I have a new problem the car idles fine (could idle
better but it idles good) but once I put it into first and ease out of the clutch it
starts to back fire, and not one or two back fires, but constantly. And I've been
asked about the values but I've checked them and re set them 4 times now. A
friend told me that it could be the pcm or along those lines because the car has
the egr deleted, bigger injectors,  a mild com cam with liters. And thinks there
was atune one it and if so could the pcm be the source  of my problem? I want
to get the skipshift delete on it as well but just wondering if it's the pcm