Ok then, running 2k at 70 mph on 5th.... that's a different story.... what year is your TJ, they used different trannies throughout the TJ production years, either way you have a standard so this should be less an issue. You are definitely geared a bit in the high side ( or low depending how you look at it, lol). At 70 mph on 5th you should be at least 2300 rpm to be the engine power band, and better fuel millage. I'd say your engine is running fine, especialy if you say in 4th it's fine , except running a bit high rpm for that speed.
When you say you are running 70 mph, is that actual speed via a gps or your speedo? Reason I'm asking is you have bigger tire size so OEM speedometer set up would be off. Good thing about TJ, this is an easy adjustment by changing the plastic gear at the transmission pick up unit, 20 minute job.
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