My 98 yukon 136k miles was diagnosed with a bad #5 cylinder. The reading came to be 90psi. Is it possible in any way that this could have been misdiagnosed? Is an engine rebuild or swap(remanufactured) the only way to solve this problem?

It sure sounds reliable, if it was done by a reputable mechanic or service tech, the fact that he knows exactly what the pressure was, would indicate that he did the test.

There are exceptions to every rule, but I would guess that he was telling you the truth.

I don't know of any fast or easy or cheap fix for that.

OK it has been recommende that I do a cylinder leak test to show exactly wear the problem is located. The test shows whether the problem is with the intake valve, exhaust valve, piston rings, or head gasket. Thing I would like to know is with either of those choses will it still need to be rebuilt or would any of them be fixable without doing a rebuild?

All would require a rebuild, except head gasket.

ok it has been recommende that i do a cylinder leak test to show exactly wear the problem is located. The test shows wether the problem is with the intake valve, exhaust valve, piston rings, or head gasket. Thing i would like to know is with either of those choses will it still need to be rebuilt or would any of them be fixable without doing a rebuild?
If it turns out to be either an intake or exhaust valve, the cylinder head has to come off the repair that issue.
If it is a failed head gasket, the cylinder head would likely be tested by a machine shop to make certain it is usable.
If the rings are leaking compression back into the crankcase, you would have numerous symptoms: possible oil comsumption, oil forced through the PCV and into the air cleaner, etc.
What drivability symptoms made you take your vehicle in for testing? Was it running poorly/misfiring? Are you using excessive amounts of oil or coolant? Fouling that cylinder's spark plug?

I don't know about other states but in baton rouge,la your vehicle has to pass an emissions test. With the engine light on I could not pass inspection. So after getting codes ran I proceeded to correct the issue(tune up, and injectors). Well after fixing those problems a new problem arose which was cylinder 5 misfire. The mechanic checked it out and did a compression check which he found out that #5 was reading at 90 psi. He recommended I rebuild the engine. A week later while driving it started to kill on me and I noticed the oil was kind of low. I had talk to a friend of a friend who looked at my vehicle said I don't need to rebuild. So then upon talking with an uncle(mechanic) from out of state he said to see about get a cylinder leak down test.

After having the lower intake done in November I noticed I have to add coolant about every month or so. The vehicle has had a miss in it every since the first part of last year.

OK One last question that should put this to rest for me. The vehicle was scanned for trouble codes and it showed cylinder misfire #5. Then they did a compression check on #5 only which read 90 psi. Should they have checked just that cylinder or have checked all of them to get a better idea of what problem they were looking at?

All.

All.
Agreed.

All.

Period.

If they wanted to give you enough information to determine if the engine is fixable, or needs replaced, the diagnostics should be thorough.
I would provide, and expect, nothing less.

They could, with little effort, provide you with options, too.

Let us know...