Gas Mileage / Oil Pressure Issues

Ok.  So it's really cold in Wyoming during winter.  That being said, I put 5w-30 qtorque in my jeep due to the temperature lows.  After I have been doing that, my oil pressure has been riding 75-above 80.  My mileage hasn't been as great on the highway either 17-18 vs 20-21.  However, I just brushed it off as the drive I usually make involves quite a bit of windy and a lot of uphill driving (4 banger...).  

Then, I just read about the Why-J and how the oil was too high and he replaced the sending unit to make it go back to normal.  I'm wondering if I need this done or if 5w-30 rather than 10w-30 is the problem.

Thanks  

5W-30 vs. 10W-30 wont make very much difference. What was your oil pressure before the change? And your lucky to be getting 20mpg out of that 2.5.  
Get a real jeep! (pre '75)

It was around 45-60 or so if I remember correctly.  

Not sure how it could be the oil. You may have the same problem with the sending unit as his.  
Get a real jeep! (pre '75)

Would that affect mileage?

I also have kind of a weird question if anyone knows.  Well, due to the hills (I mean quite a few long and steep ones...) My jeep seems to do well once it's "warmed up" and I can stay at about 55-60mph in gear 4.  However, after a while, it seems as if it is "tired" if you will and I have to start using gear 3 or I'll fall to the 40's.  

Is this the sending unit as well?  Or is it just the hills themselves being a pain?

Thanks.  

No the sending unit wont affect mileage. Not sure what could be causing that problem. A sending unit wont affect the way it runs either. A sending unit only affects how the gauge reads.  
Get a real jeep! (pre '75)

Oh.  I was wondering about that.  Oh well I guess.  I be doomed until I (if ever) get the engine I want swapped in, haha.  

What are you planning to swap into it?  
Get a real jeep! (pre '75)

Well, ideally, a diesel of some form, like the 3.0l crd in the grands would be fantastic!  However, given the price, they are not really feasible at the moment.  I will probably try and get the 2.4l 4-cyl that they use in the patriot.  It has 175hp, 165 ft/lb of torque and gets 28 on the highway.  Granted, my jeep is geared lower than a patriot but due to the vvt and whatnot it should be mid to low twenties and the power boost will be welcome.  

This won't happen any time soon and by the time I get around to do it I might be able to afford a diesel  So we'll have to see.  

Hope it goes well. Thats a good powerplant to swap to a TJ. Ive never really thought about the 3.0s before as a viable option. How much would one run in good shape?  
Get a real jeep! (pre '75)

I just found one in nice shape for $5500.  

Yieks. thats out of my price range lol. Is it compleat with the wiring harness and computer? And will you be doing the swap yourself?  
Get a real jeep! (pre '75)

Yeah, it is complete.  I know it is a lot, that's why I was saying the 2.4l is a more viable option.  I found one a while back with everything for $375 on ebay :/ and couldn't afford it because, alas, I am a broke college T-T It's very sad  I have a long project list after I take a couple auto classes and welding and I will have a cornucopia of jeeps haha.  I would love to get my hands on a scrambler and v-8 it and maybe a flattie too.  Who knows what the future holds eh?  

P.S.  Besides, the YJ, while many consider the "wrongler" and many other sad names is a capable vehicle with the right suspension and build like any other jeep.  Besides, I see more "real" jeeps with coilovers and/or coil conversions these days and that gets away from what the CJ's were imo.  

In the last two weeks - I've experienced my Oil gauge upon startup going all the way to 80 & staying there. The only change is when I brake and/or come to a stop. Then it stays steady around 60. Once I accelerate, it goes right back up to 80/max. I just changed my oil - and no change in behavior! *grr*

I am not experiencing any strange sounds or having a lack of performance.

My Jeep is a 2000 TJ Sahara, stock engine, etc.

Any worst case scenarios & suggestions are appreciated!