I am a COMPLETE novice, but trying to learn and do what I can on my own.

My '01 recently seized up and a buddy determined it was the AC pump. Replaced the belt with the bypass version. A month later, I moved across the state to Iowa. A couple weeks into living here I turned the truck on and it was idling really high (about 2500-3000) but would settle down to around 1100 when put in gear. However, shifting into gear is causing a progressively worse "jump" into gear. Hadn't really had the money or the time to take it in so I let it mostly sit unless I absolutely needed the truck.
Today, the idle is still high and does seem to cycle a bit in that it will rev up close to 3000 then settle back down around 2200 or so and then rev back up again and so on. I backed it down the drive into the sun for a little warmth and it darn near jumped a foot when I shifted. I turned the heater on defrost so I could clear the windshield and absolutely nothing came out.
I can't get into a garage for a few days to get it hooked up for diagnostics. So I thought I'd try here. My research leads me to think part of my problem may be a vacuum leak and/or maybe a sensor somewhere. I'm open to ideas and suggestions. Just make them simple for a nearly complete novice to follow, you know, like I'm a 5th grader.
Thanks!

 

Told you I was a novice...
F250 SD, 2001, 5.4L, V8 crew cab. About 170K miles.

 

Yup, sounds like a vacuum leak.

I'd start looking underhood for loose hoses, disconnected hoses, broken hose nipples, etc.

 

So, I read through the forums on similar issues and somewhere along the line someone mentioned resetting the computer. So I did.
Idle is now behaving (for now, I assume) and the hard shift jump is not present. After about half an hour of run time, the heater blower finally came on.

So, what might be the root of my issue here? Still vacuum?
Thanks

I did look for anything loose or off and haven't found anything.

 

Right back where I started. I went 20 miles up the road and not even halfway the truck started revving up while driving. Even in cruise it would fluctuate from around 1700-2300 rpms. Made it but as soon as I put it in park it worked its way from around 800 up to 2000 or so and would stay there. Currently sits at just under 1000 in gear sitting still.
Thoughts?