Blazer 95 trans slipping
 

When I drive and need to accelerate slightly, RPM go up a few hundred before it begins to accelerate. Especially when I start driving on hills RPM goes very much up. This happens in both "D" and "OD". Does anyone know if this is correct, or if the transmission slipping.

A 300 RPM spike between shifts is a "slip", but if your at a dead stop and it takes a few hundred RPM just to get moving then that is somewhat normal. On a level surface does the truck move on its own in gear without you pressing the pedal?

If you are moving at any pace does it spike in a few hundred RPM (like its at 2500, then it shifts it jumps to 2700 or 2800 before going to 1800 or 2000); then that is not normal and can cause a transmission to overheat and damage itself. Usually that because a low fluid level in the transmission, and there is a specific way to check the automatic trans fluid level (usually it tells you in the owners manual or repair manual if you have one). If it is low just add the proper amount of fluid, but do place a piece of cardboard or a steel pan under the transmission to check if is leaking.

If the fluid level is okay, and the transmission still slips, then find a way to check the transmission temperature. An overheating transmission can cause the engine to overheat and can even cause a check engine light. A trans that is overheating, with the correct fluid level and is under light load, is usually failing transmission.

If the trans is good, then maybe consider getting a low RPM stall torque converter. Most factory converters are designed with engine, the faster the engine the higher the stall on torque converter, I believe that the factory converter with most of engines is around 1500 to 1800 RPM, you can get 1200 RPM stall converter if want more grab at slower engine speeds.

Thanks for the reply.
On a flat surface when I release gas pedal the speed will decrease gradually.
But what I have noticed is that when I drive on a flat surface and begin to drive up a hill in the same gear, RPM goes up some hundred to keep the the speed. I do not know if it could be the booster valve that is worn, so I do not get enough pressure in the gearbox.

Again, that sounds kinda normal. Maybe try shifting into lower gear when you driving uphill like second of even first if you are driving slow enough. The torque converter will always have some give until the torque converter locking clutch applies, and sometimes shifting in to a lower gear can cause the clutch to apply earlier.

The main item you want to look at is the transmission temperature. If the transmission is not opperating correctly it will overheat.