I believe it, then again I also have an 86 Chevy K5 Blazer tucked away in my garage with 29,000 miles!
OP you realy do need to find a mechanic you can trust to look at it. Like other said do a compression test and go from there. The oil additives only extend a problem NOT cure a problem, Lucas and STP and such work great to thicken oil and will help quit a rod knock or piston slap but only until parts break so use with caution!
Years ago there was a product called "lifter looser" or something like that, it was a solvent based product that dissolved gum and varnish and would free up rings and lifters. It did work but remember that sldge and junk has to go somewhere and that somewhere is the oil filter so change it often when using a solvent based cleaner.