I had a similar problem and it was my gas cap. Replaced and no problems since.
4" Teraflex long arm lift. D30 tubed with chromoly axles, high pinion, powertrax no-slip and Warn Lockout Hubs. D35 w/ultimate 35 upgrade OX locker, 4.56 gears. NP231HD, Air on Board, Warn M8000 Winch.