My 05 sport trac started having this problem for a few months now. I noticed that this only happens when the engine is still cold. I'll let the engine run for about a minute or so, put it on drive and sometimes it takes a about 5-10 seconds to go in gear. pressing on accelerator for a couple seconds, and then suddenly lurch(shudder) forward.

Sometimes it engages smoothly from park, and as I start driving, it will slip out of gear again(foot on gas and I'm not going any faster despite the RPM going higher on the tachometer), then a couple seconds later; I lurch forward again. Has anyone experienced this issue?

 

Might be a good idea to have the trans fluid level checked. When was the trans last serviced?

 

I don't think it's ever been serviced. I've had it for two years and it was one owner before that. It has 95k miles on it. But I will look into having the level checked and serviced. Thanks

 

The most simple cause could be a clogged filter. Cold fluid would be more difficult to pass through than warm fluid.Also, by dropping the pan, you could see if any abnormal amount of debris has collected on the pan's bottom.