97 tahoe with a hiccup at 40-45mph

ok....i had dream 2.5" from the manifold back performance exhaust put on and eliminated my cats....so my truck threw a code ((catalyst efficency below threshhold "bank 2"))...now i herd about this "o2 simulator" and i put it on, works great, it and took my truck out of limp mode.. but i still have that hiccup at 40-45mph..also at a red light when the engine is kinda cold it will get this power burst were it wants to lung foward for a second...i have replaced....distributor, cap, rotorbutton, wires(bosh), plugs<~bosh platinum+2,...now im down to..
1.ignition coil
2.injectors
3.fuel pressure check&fuel filter
very confused any info will be very appreciated..
ALSO HAVE SET OF FOUR 33-12.50-15 PROCOMP MUD TERRAIN TIRES FOR SALE 95% TREAD PAID $625 ASKING $500