I have a 2000 Ford 7.3 lifted 6" with 37" tires. I purchased a 35' Toyhauler and I continue having trouble pulling grades with my tranny. I have full synthetic and have added greater capacity cooler onto front of radiator. Tranny reaches 220-240 degrees and wants to keep rising. I had to stop half way up the last grade I pulled due to my temp. What can I do to assist my truck in pulling this beast?