Hesitation, Temperature Gauge Problem

[afooten]

My 2000 Nissan Xterra has been acting strange lately, recently i replaced the valve cover gaskets, now any time you go from a dead stop to accelerate you have to stomp on the pedal to get any where there is a big hesitation, my fiance thought it was the vacuum lines getting to much air, then he said the code reader is coming up that its the vacuum lines and the knock sensor, a friend of his said the catalytic converter could be going bad and that would send all sorts of codes like the vacuum and knock sensor and to look under the truck at night after we do a couple start stop runs to see if it was glowing cherry red, well it wasn't (no surprise there lol) i noticed the last two days that every time i kick the truck out of overdrive or even romp into it and go over 3000 rpms my temperature gauge goes down...once i get into the gear it needs to be in and the rpms go back down the temp goes to the middle....if any one has and knowledge or experienced this before let me know...its very frustrating not knowing what to fix

[Rev_D21]

A bad temp sensor can cause problems like this. There should be a test procedure for the sensor in the FSM. www.nicoclub.com/FSM.