[Sburn]

Originally Posted by Mister B

I have a 2004 F150 XL 4x4, 3.55 gears, Automatic transmission and 4.6L engine with 136,000 miles. I've owned it since new.

My truck basically drives and shifts fine on the open road with no traffic. It's mostly when I am in heavy traffic when I constantly have to adjust, letting up and then getting back into the throttle, compensating for traffic around me that it hesitates like it does not know what gear to shift into (it has done this pretty much since new). If I take it out of overdrive it acts a little better. Also if I am accelerating down an on-ramp to a highway and let off the throttle for a second...

Same truck as yours, 4.6L and 3.55, but 2007 and 4X2. The above part of your post describes perfectly my impression of the stock transmission behavior. Before adding a Gryphon, that's the way mine acted since new.

....and then hurry up and get back into the throttle to try and merge into traffic, the engine sometimes revs up and acts like it is in neutral and then after what seems like seconds it harshly shifts into gear and then begins accelerating.

Thank you,
Brian

But the second part of your post makes me agree with the other posters in that you should rule out any mechanical issues. I'm referring to your use of the word, "seconds". I'd say the stock trans does pause a bit between grears, but I only ever felt it to be a fraction of a second.