RPMs surging at freeway speeds

[drewgibs]

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

[herkyhawki]

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

[skiboyne]

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...

[Floyd_ODB]

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