Underheating problem!

95 Chevy astro/4.3 l with 111K and the coolant never gets hot. Max temp is about 120 f. Both on the gauge and with a thermometer in the radiator cap opening. I have too much anti-freeze to water ratio about 70% and wondering perhaps a small leak into the intake or combustion area. I noticed a slight hesitation/miss upon acceleration usually up a hill. If I put my hand by the tailpipe, my hand feels a bit damp and sticky like antifreeze, though coolant loss is quite mimimal-1 qt per 2-3k miles. Any suggestions are much appreciated!