hey guys, im sure this issue has already been adressed but i dont have much time and i need your help! i drive a 2005 f550 rollback towtruck, its got the 6.0 in it, well long story short, its got is 3rd motor put in, 2nd one had a cracked block. now this 3rd one is used but it had low miles on it. anyways the issue is, is that when we put it in it would over heat if idleing for a while or casual driving, so my mechanic and i replaced the temp sensor, thermostat and radiator fan due to it not coming on, anyways he got this all done and took it for a rip with his computer hooked up in it, he drove it pretty rough and the truck said it was over heating but his computer said 192 degrees F.... so we are stumped, also i notice it will do that when ever there is any load on it, heres exactly what its doing, it now idles fine and doesnt overheat at idel, put any load on it and drive it with rpms over 2000 and it will say "CHECK GAUGES" but the coolant temp wont rise right off, then it instantly jumps to (H), i pull over and pop the hood, sure its warm but its not hot like it says and the coolant tank IS NOT puking coolant. so while the truck says its hot, i now have no power due to it going into limp mode and if i continue to just drive it the gauge will instatly fall back to normal temp, it does this ever 20 mins for about 20 mins if im on the interstate doing 70-75. I have flushed to coolant system and also the heat isnt super hot when i turn it on when it says its over heating like it would be if it was... so long story short, it says its overheating but its not, and when its doing that it goes into limp mode. and the coolant is clean with no oil in it, oil is clean with no coolant, truck has egr delete, it does however have an exhaust leak somehwere near the manifold, and sometime it will take a little bit on take off to build boost. its really stressing me out due to it not being reliable, if there is a state police call or accident i cant depend on this thing. i love this truck itsself but the motor is pissing me off... lol. can someone please help. what am i missing here? i dont think its head gasket or injectors, and another thing is, it will randomly idel a little bad, like at red lights it may run great or may not... what is it? anyone else have this issue? whats the fix?