My truck is a gas job has the 4l80 and around town it does ok but still gets hot put a big cooler on last nite and It still has an issue the pressure line is hot and the return and cooler is cold as ice it's around 40 degrees herey pressure line is hard as a rock and return is soft after its warms and the cooler is new and has not blockage any ideas would greatly be appreciated

 

Ive heard of this happening alot to 2500hd owners, when was the last time you had the fluid flushed?

 

I'd suggest pull the cooling lines off, and MAKE SURE you didn't leave a shipping plug in it.

 

So the fluid itself could do it

 

After re reading your original post, im starting to seriously believe their is something in that pressure line.. It sounds like the fluid is struggling to move in the line instead of flowing almost freely.

 

I've puller the return off my cooler and the fluid shot out I've also pulled the return off the trans it's self cleaned it out still same thing like if it wasn't get flow at all u would think it would heat up quickly but it don't it take a lil while to over heat I can go about 30 miles on the interstate and it slowly moves up but still will cook