Daktowmygetting to hot
 

every time I get on the gas to go up hills on the freeway my truck starts to get hot. The temp gauge starts to get really close to the red, I always put the heater on and drive slower, it cools down a little bit. I can sit at stop lights or drive throughs with the a/c on and no issues.

Have you had the cooling system serviced?

Yes, I flushed the system, checked the thermo, replaced the radiator, I have the correct psi cap for the radiator. Everything is in good shape but I'm lost as to why it's doing this.

one issue, go check your fan, if it spins freely with no resistance, the clutch is shot, once the motor is under load and fan is not working properly this would happen

What Superdak05 said.

Also, get the coolant checked for the presence (or hopefully the absence!) of exhaust gasses.

I had a Cavalier-class car once that did that. Turns out we had a minor leak in the head gasket - under full pressure (like driving at speed), exhaust gas would bubble into the water jacket.

(Odds are the fan clutch - but thing is, at speed, the air through the radiator should keep it cool enough!)

Oh, and one more thing you didn't mention - how is the radiator as to "leaves, bugs, and mud" stuck into it on the OUTSIDE? A lot of people will flush the cooling system INSIDE, but leave a pile of crap between the condenser and the radiator ...

RwP

RwP

^^^ Would be my first guess. Second would be you didn't replace hoses when you replaced radiator and a worn hose is collapsing under load...

hammer you are correct when I replaced the radiator with a new one, I did not replace the hoses. I'll check the fan today, hopefully it's not a head gasket. Thanks guys

You have a bad head gasket and or cracked head!

Entirely possible especially since we don't know what prompted the radiator replacement. But a lot of less traumatic things can cause the same issue. As stated, I've seen more than once using old hoses, a worn pressure hose collapse under load and limit coolant flow.

However, it'd be a good thing to check oil for coolant and vise versa...

this is my first newer vehicle and it's driving me nuts! fan clutch is good, hose has a spring in it so it won't cave in and is not caving in at full throttle. I drove to plamdale on Saturday 40 miles it's a desert about 2500 ft up that was about 100 degrees no issues! just drove to jack in the box 4 miles away almost had to turn on the heater. The new thing that popped up today is a crap load of codes mostly transmission codes and a few engine here's what I wrote down before they went away P0988, P0700, P1603, P0700 , then the TCM had lost signal what the freak is up with this truck, I also have the shimmes like in the post about slowing down at high way speeds. truck has 139k and is a 06 made in September of 05 I have already put a solenoid pack in the transmission changed the fluid and I take good care of the truck