my 97 cherokee 4.0 is having major problems after reading the self diagnosis codes i have replaced the TPS, CPS, MAP, o2 (downstream one), and VSS sensor along with new spark plugs and wires, but it still runs bad so heres how its running, at cold startup it runs perfect idles nice and drives nice til i hit 5th gear, then its nice and warmed up and it loses all power and pops and pings in the engine area like its backfireing only when warm, with all the new sensors replaced there is no check engine light. so im sittin in my driveway holding it around 2500 rpms for like 10 mins or less hoping it would just clear up but it like pullses or something and then suddenly i notice smoke inside under the carpet the muffler got way to hot obviously , does anybody know if its distributor related? oh yeah if i drive it with the pedal to floor it seems fine but only all the way to the ground not half way all the way... please someone help!