Recently my truck started hesitating when given gas in overdrive there's no response from the engine rpms don't move as well as current MPG and the truck will slow down going down hill. The only way to get it to go is to floor the gas pedal several times before it takes off it only does it when the engine is at operating temp it runs fine on a cold engine. I recently had to replace the alternator after it went bad. The transmission still shifts smoothly and there haven't been any codes given the engine is a brand new crate engine with less then 6000 miles the transmission is original with 182k miles. It doesn't feel like the tranny is slipping but more like a delay between the pedal and the engine it does nothing for around 10 seconds then i can hear it rev up and take off. It's a 2005 f150 4x4 lariat

 

It also progressively gets worse the longer i drive and then goes away for about 100 miles after i disconnect the battery