I have a question regarding long term storage and degraded performance. My 88 spent most of the last 13 years in storage. Ive since pulled it out and have driven regularly for the last 18 months, following a rather thorough tune up, and all fluids, filters,plugs and wires, cap and rotor ect. replacement. This car, aside from an aftermarket cat back exhaust, is completely stock and has 54,000 original miles. (5.7 and 700r4). Lately, the car seems to have about half power, has developed a slight "miss", and runs very poorly, most noticeably below 2200 rpm. Performance seems to worsten the warmer or hotter the car gets. My senses point to the TPI unit, or related. My question is, given the age of everything involved, is it better to remove, rebuild and/or replace all of the sensors, gaskets, and all that is related from the intake manifold up? or am I overthinking this problem?
Your expertise(s) is much appreciated.

My 89 Formula 350 that has 40K original miles spent the last 2 years in my garage without running, so a few weeks ago I decided to start it with no avail. I finally got it running with carb clean and I guess I got the injectors to clean out enough to let it run, not very well though. I siphoned out as much gas as I could, and added fresh gas and did a full tune up on it. After driving a while it got better, but no where near as well as it should, so I just pulled the plenum and runners and am in the process of changing the injectors. I think they are just to gummed up to run right, and I've read the stock injectors aren't that great to begin with. Im hopping this fixes the problem. Yours could be injectors or maybe fuel pressure regulator diaphragm. Just my guess but Im no mechanic. Good luck

The 2 biggest problems with long term storage are humidity and degrading fuel. Humidity corrodes electrical connections. Old fuel changes checmically and will damage anything it touches. Cars can sit for long periods of time if they are properly perpared, but unfortunately it rarely happens becuase the "sitting" is usually intended to be temporary.

These issues can be reversed, but it might take some time and some new parts.

Yeah once I get her running she won't sit like that again without driving her every once and a while.

Thanks to you all for your responses, and as expected good advice.