i have a 01 qx4 and it has started to surge under load before it shifts. it started about 4 months ago and has gotten worse. before it started that i got some type of catalyst problem code, i cant remember the exact code, i reset it and it came back on and then went off on its on and has not been back on. before this problem i had no problem acc. up to cut off at 105mph now it will only go up to about 95. i had the trans. fluid flushed (but not filter) and didnt help. next i will change trans. filter and fluid again. also need to change plugs. anyone know what is involved in changing plugs? ie intake manafold, or trans. prob.? the truck has 86k. please help.