Chime while towing uphill
 

I got my 03 6l with 112k miles on her & I did the egr delete, new oil cooler, coolant filtration kit and ficm with the atlas tune. I was towing my trailer up the pass and I faintly heard a chime that I thought was coming from my stereo, turned my stereo off and could still hear the chime.'mmi thought that it may
Be some sort of warning. Then I realized that this chime was only there when
My foot was in the throttle 100% and going up hill. My truck was not over heating and running fine with no known problems.

Anyone know what
This chime is? Mi think its some sort of warning ????