i had something similiar happen to mine. make sure that the 2wd/4wd switch is making contact. the rubber around the switch will dryrot and let moisture in corroding your connection. take the switch apart and clean it up good with contact cleaner and sqirt some dielectric grease on it. it fixed mine for about 3 months but the oxidation was so bad i had to just replace the switch. its only about 30bucks so not bad. im not saying thats what it is but its somewhere to start looking, plus its probably good to clean it up anyway from time to time.
BILLET GAS CAP
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