RPMs surging at freeway speeds

96 blazer 4wd 150k miles vin W
just wondering if this happens to anyone else, at freeway speeds usualy climbing a slight hill, the rpms at around 2k will drop down to like 1800 and surge back up, and i can feel it surging, without changing the position of the gas pedal at all. i have to give it more gas, sometimes enough to make it drop down a gear, and it goes away. i thought it might have been the fuel pump but i just replaced that about a week ago and it didn't really change anything....could this be something with the injectors, tranny, or vacuum system? anyone have any ideas?

thanks
drew

You may be noticing the Torque converter lock / unlocking. Normal stuff.

Just another thing to check, this sounds a lot like planetary gears going bad in the tranny. I would have a shop at least check it out...

my dads '96 did the same thing traveling in the mountains out west. I also could hear bubbling water(boiling)where the tranny lines entered the radiator core