Cherokee Owners,...A little help,...pleaze

Tryin to figure out why my old dependable 99 4.0 Cherokee has a lean dead spot when It goes from closed to open loop,...feels like its goin way lean for about 1/2 mile or 30 seconds or so,(coughs and backfires through the throttle body). Rain or shine. Doesn't stall, but It wants to,..Revs great when I depress the clutch. Put a scanner on It,...No Codes or engine light,....O2 is switching fine,...Distributor pick-ups are intact,...mileage is good,...no black smoke. Has new plugs, Cap,rotor, and wires,...Does It shortly after cold startup, and after sittin for for a short time,...then It runs like a raped ape,...I'm feelin like Its an AIS or TPS issue,...anyone else have this prob,...