Jeep Cherokee XJ 2000 4.0L Auto 151,000 Miles

Before I go into the details, I must first explain that I have an ongoing issue with my Jeep.
When starting from cold it works fine for the first few 100 yards until I reach the main road and then when I try to accelerate away the engine stutters, loses power and then something seems to click over and then it's fine for the rest of the journey.

I took it to the local Jeep dealer and although they cleaned out the dirt from the ignition unit (which means it now idles much nicer) I still have this issue and cannot get to the bottom of it. A friend did mention that could it be the stepper motor which switches from cold to hot running??
Anyway, it was cold tonight leaving work (6 degrees) and the place that the Jeep would normally stutter and click over didn't happen tonight, instead it stalled and I had to slip it into neutral and re-start (which took a bit of effort) but it was ok after that.

Any advice??

Also, I think there's a problem with the power steering - it's making a whining noise when parking now (no noise when driving normally). I've checked the power steering fluid and it's fine, could it be the power steering pump?

Thanks in advance!