my truck at speeds between 20-45 will slip if i try to cruz. RPMs will be around 1500 and the truck speed drops unless you run the rpms up to 1800 ? and the shifts take to long, it drags them out?

 

sounds like line pressure.

 

x2 with pressure

If your talking about the truck in your info, the 4R100 transmissions (mostly all Ford transmissions for that matter) have soft, car like shifts. this "luxury" shifting can only be achieved by slipping the clutches for each gear in slowly, rather than just slamming them together and getting what's known as a "bang".

But what your describing, sounds like a failing pump or a SEVERLY clogged filter (by severly clogged, i mean it holds fluid like putting a shop vac to a flat piece of sheet metal). How many miles are on the truck/transmission? What's your maintenance habits with the transmission? And have you checked the fluid level? Does it smell burnt?

 

had the trans flushed this week. problem accures at 1500 rps everytime. only has 80k on it.

 

Did they Change the filter when they did the flush? Was that the first time the fluid was changed? ( I ask because A LOT of people neglect the transmission until they decide one day, usually 4 years too late, that they wanna change the trans fluid)

Any mods done to the truck?

 

they only changed the fluid

 

when was the last time the filter was changed? if fluid level is good and the filter is clean and clear, it sounds like your pump isnt creating enough pressure to hold your clutches in, resulting in your slipping.

 

well just doesnt make since it pulls at 1200rpm but not 1500?

 

Your engine really doesnt reach its torque curve until you start getting around or above 1500rpm. In this case I just think 1500rpm is just the spot where it breaks loose.