The Nissan Path

help can any tell me the cause of the following problem?
95 XE v6 4x4 a/t 3.0 after a tune up runs good when cold when warms up runs poorly spits studders gas milage the same as a hum v 5 gal. to the mile
just had a new exhaust system put in new cat muff and dual tail pipes
help b/4 inwreck it or burn it thanks pre tune up ran ok with a little studdering now and then. plug ngk tried bosh iridium run worse faster
changed rotor and cap 2x plugs 1x wires ok checked with meter

Sounds like a sensor or timing issue.

well after about a month of trying to figure out just what the problem is
and spending endless amounts of hours under the truck and at the junkyards I have finally resolved the issue I had with the sputtering and backfiring I changed the 02 sensor to no avail also changed temp sensor
checked just about every sensor on the truck the culprit? the cam angle sensor. when I removed the cover it had a rust colored dust on it and when I removed the degree wheel it appeared that the center had electrical burns on it well I cleaned everything off and replaced all the bad
parts with parts from the junkyard. replaced everything started it up and it ran better then before............... What idid notice was that a spring washer was missing in the original set up, that was replaced and all is good thanks to everyone that sent a suggestion and to SKYE for his input thanks

There is a link somewhere that shows the grounding wire on the MAF sensor goes bad. Do a search. Nissan offers a wire harness to fix this also.