Hi all

I've got a 91 Firebird 3.1 V6 and I've been chasing this problem for months now. It was virtually undriveable as it was hesitating and bucking when trying to drive it at all but I've replaced tons of stuff on it so far in the process of testing things.

new fuel pump (previous owner done this)
new fuel filter
New fuel injectors
New fuel pressure regulator
New MAP sensor
New TPS
New IAC
New distributor
new plugs
new leads
new knock sensor.
new vacuum lines where needed.

Fuel pressure is 40psi with the key on and holds nicely. 38psi when running and stays at 38psi no matter what rpm you rev it to. Timing set at 10 degrees. I've tried two spare ECUs I managed to get from a friend. Cleaned all the ground wires.... and it still sits there running lumpy! and after it's been running for about 10 minutes it will randomly drop rpms then gradually recover. Then do it again at different times.... that's the really weird thing in all this

however it seems to drive fine now. It feels nice and smooth when you get going but as you slow to a stop you can feel it get rough again, it doesn't cut out or anything but something still isn't right. I'm not sure where to go from here!