1990 Ford F-150 Engine Issues

I own a 1990 Ford F-150 XLT Lariat Super Cab 4x4 (LWB). It has a 5.0L EFI V-8.

Here is the issue:

Three weeks ago, I had some issues with it starting for the first time. We have owned this car since it was new and hardly ever have we had to use the gas pedal to get it to successfully start. Since then, it has been a regular occurrence that when I start it for the first time everyday, I have to push the gas pedal down slightly. I didn’t think much of it until last week when, after starting but still in park, the RPM’s move up and down a lot. It goes from about 300-700 RPM, up and down while the engine idles. Today, I was pulling out of a parking space and realized that I had almost no power. I had my foot on the pedal, and it was hardly moving. The RPM’s wouldn’t go past 1000. I parked it, turned it off, and let it rest for about 5 minutes before starting it again, and it then was ‘fine.’ (‘Fine’ as in it was the same as last week). I immediately drove to my auto parts shop to see if they could run a diagnostic, which to my chagrin the could not because their tools were not functioning. I called for a family member to come pick me up, since I could not get the truck to run ‘normal’ again, and when my father arrived, he tried to drive it around the parking lot. He found that at lower RPM’s, you had to ‘feather’ the gas pedal in order to gain speed and RPM’s, and once you broke about 1000 RPM’s, if acted normally. The hard part is just getting it to break that threshold of 1000 RPM’s.

Can anyone help? Thanks in advance.