1999 Chevy Suburban

111k 1999 Suburban - everything fine expect when I try to pass or start out from a stop at a quick pace.
when I do either of the above... feels like it doesn't get enough gas but the RPMs go up.

[color=blue:3dcd847ed5]example - passing a car... passing gear [i:3dcd847ed5]sounds[/i:3dcd847ed5] like it wants to go but the speed remains the same.[/color:3dcd847ed5]

[color=blue:3dcd847ed5]example - quick take off - also [i:3dcd847ed5]sounds[/i:3dcd847ed5] like RPMs are up but the speed is limited.[/color:3dcd847ed5]

Reminds me of trying to pull away with something heavy on the back - if that makes any sense???

Thanks -