99 Ford Ranger 300k miles but well kept. 90% of miles are highway. Changed oil/ 3000 miles. Started to run rough no past history of this. Thought I got bad gas, changed fuel filter plus high octane gas with two bottles of dry gas. Seems better but not 100% right. When driving up steep grades have to shift down to make grade also in 4th or 5th gear around 60+ mph it feels sluggished had tune up month prior to this issue. Any ideas? Thanks