When I am towing, after I go 15-30 miles my truck loses power and it won't go over 55- 60 mph. Once the trailer is off it works fine, the other day it completely quit running, the fuel injection rail and one injector was replaced, now it runs fine.. except when towing. Now the other day my ac started to blowing out of the defrost vents when you first start the truck and after a few minutes starts to come out the front vents, and it isn't blowing very cold!

 

Have you checked you oil temp to see how high it is running

 

I was towing a trailer again on Friday and it lost power again.n I took it to the shop and they said they think it is the head gaskets, told me they won't do them so have to find a diesel shop to do it. Not thrilled to find out how much that is going to cost! I have not checked the oil temp before, what is normal operating temp?

 

oil temp should be within 10-15 degree's of you engine coolant temp