Headed for a weekend trip. Pulling a steady incline for about 10 miles. No matter what tune I run it wants to run steady 1250+ to maintain 70 in 5th. Pulling about 8,000 pounds. As it got steeper for the last mile It ran at 1300 and up and 230 plus. Fan was screaming away and it wouldn't cool off. Hit the top of the hill at 236 and it finally started cooling off after we went down hill. What would be causing this? Turbos are running very close to a 3:1 ratio on boost. Was running about 30 psi steady on the last steep mile.