Towing / overheating ????

Ok, while towing my enclosed trailer last night I heard what appeared to be a boiling fluid/water sound coming from the dashboard. This may be stupid but I put my ear to the tranny console in the truck to see if the sound was coming from there and it wasnt. I also got under the truck in the area of the tranny itself and couldnt hear the sound either. I think it was near the fire wall area. It was a very faint sound, and I could only hear it when the engine was turned off and there were no other noises. I towed my trailer and bike (2000 pounds) for a total of 430 miles mainly on the interstate. I used third gear and did not place the lever in Drive. My average speed was 63 mph. My average rpm was 2800, but would rarely let it go over 3000 because I wanted to conserve fuel. At first I was thinking that it was the tranny fluid, but when I pulled the dipstick the fluid was lukewarm at best and touchable. Accually I ran my fingers down the entire dipstick and it was also lukewarm. As I listened closely I still heard the faint boiling sound though. So I began to feel different parts of the engine that I could touch without getting burned (now keep in mind I just stopped) so the engine was hot. My engine temp. gauge was where it always is whenever I drive and that was in the middle of the H & C markers. After feeling around for a little while I noticed that the only part that appeared to be warmer than usual were the two rubber hoses that lead into the firewall. If I stand facing my truck from the front and looking at my engine these two hoses are on the right side of the engine. The same side as the oil and tranny dipsticks.
These hoses were down right hot. I could not hold/touch them very long. I may be wrong but I think they lead into the heatercore behind the firewall. (I did run my defroster on warm last night because it was cool outside.) The engine coolant in the reservoir (spelling?) was not boiling and there was no smoke or anything. The tranny was shifting smoothly the entire time, but as I stated I had it in third gear. The engine was performing normally and no indicator lamps came on. This was my first time towing under a load for a long distance. The terrain was for the most part flat with a few minor grades and hills, but I wasnt pushing it by anymeans. I'll take pics of the hoses I'm talking about and post later. Any thoughts??????