Having problems with my Sonata. 2000, GLS, V6, Auto, 76K. Started having problems with hesitation only when climbing hills. Would resolve by downshifting and problem would stop, shift back and would start up with hesitation. Had already ran fuel injector cleaner through the tank twice, changed air filter, pcv and it's hose, cleaned throttle body. No improvement. Today started car up and it ran rough, went about 1 mile and engine coded. Checked code and it was PO305 Cylinder 5 Misfire Detected. Spark plugs are Bosh Platinum and were replaced about 25K ago. Pulled plug 5 (not sure of order but assumed it is the center plug towards front of car) and it looked fine, neither white nor black and sooty. Checked plug wires and at coil for damage - appears fine no burnt or cracked sections. Also, oxygen sensor was replaced within the last 2K, and speed sensors were replaced at 50K.

Any mechanic wiz know what's up with this?? Thanks.