Oil Pressure Querry - again

I posted this once before and then the system went down and I can't find where the post went. Anyway...

My oil pressure is acceptable when "cold". However, the longer I drive the lower it gets. On the highway, it doesn't just drop suddenly, it creeps down to about 35psi. If I downshift, it pops back up a little above the 40psi mark. OR -- in town, when warm it will drop down to about 20psi whenever the RPMs drop under 1800, stopped or coasting. When I get them above there, the pressure is again above 40psi. Due to the in town driving, it is always going up and down quickly. A few minutes of cool down and things are better.

I have recenly changed the oil (Valvoline Durablend 10W-30) and filter. I also changed the sending unit soon after that. While this helped moderate it somewhat, it was not the cure. There is no noticable oil loss (other than a few drops on the driveway) or loss of drivability. I bought it with 60K on it and have used Durablend since -- I am now at 145K. Should I go to straight 10w-30 or is there something else I should look into? My other thought is a remote oil filter to help cool the oil. Chance this may help? And where can I relocate it to anyway (I have never liked the factory location anyway).

Current Mods (few): 3-row radiator and HD thermostat, slightly oversized 235/75/15 tires, new header, new high flow aftermarket cat, new Rusty's cat-back system w/ flowmaster muffler.

Would the new exhaust and oversized tires take it far enough out of its power band to cause the lower than usual oil pressures?

The only for sure way of getting an accurate reading of the oil pressure is with an mechanical gauge. You can run both a mechanical and electrical gauge by intalling a T block, the block screws into the block, then two other holes allow you go screw in the electrical sender and attach a tube which you can route thru the firewall into the cabin, then attach a gauge. I'm not familiar with durablend, I only run Mobil-1 and that gets run in all the vehicles.
The main reason for low oil pressure is worn main bearings mostly. The durablend is a syn/organic mix correct ?? How fast does your oil turn dark after you change it.

It sounds as if your pressure, though a little low, is probably still within the allowable range. You should check it with a good gauge to make sure, but then I wouldn't worry too much, especially if it goes above 40 when revs are up. I have found that premium oil filters such as K&N, Bosch, and Wix seem to give a little boost to the pressure. Of course heavier oil will too, but as long as the pressure is sufficient to keep the oil cushioning the bearings properly, thinner oil will flow better and that, in turn, should carry off heat better, so there's a tradeoff if you add thickness more than is necessary to keep the pressure safe.

If you mentioned what year Jeep, but 145,000 miles is hardly excessive.

The factory service manual specifies minimum oil pressure as 13 psi at idle, and 37 to 75 above 1600 RPM. Your readings are low-ish but, as Matthew indicated, essentially within spec.

What brand filter do you run? You should use Purolator or Mobil-1. DO NOT use Fram.

Why waste money on synthetic blend oil? Either run synthetic, or run oil. If you want to use conventional oil, get Castrol 20W50. If you want to run synth, try Castrol 5W50. Either should improve your oil pressure.