Engine random misfire

I own a 1999 cherolet tahoe with 184000 miles. I have had this truck for 2 years. After 6 mos. It developed a random misfire condition. I have replaced the distributor cap and rotor twice, along with 4 spark plug changes, plug wires, ignition coil, intake gaskets and fuel injector.

At around 170,000 mi. It developed a random misfire. The work I've listed was done trying to correct the misfire. Recently, it has been acting very erratically. It has always run worse in wet conditions, but now it has started to backfire badly at times. For instance, I changed the oil yesterday (mobil1, delco filter) and this morning I drove it. After about 10 min. Of driving normally, it started missing out and backfiring to the point that it wouldn't stay running without me giving it gas all the time. After sitting for 10 min. I started home, with it still running badly. Unexpectedly, halfway home, it started smoothing out and running well again. I can do the work, but I cannot find the problem that needs fixed. Any ideas? I really need my truck to run, its my only vehicle and I can't afford taking it to a mechanic.

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