Low oil pressure helped by 5w40 oil change

Your Lucas is what brought the pressure up, more than the higher viscosity of oil. Lucas is thick, probably close to 80 - 100wt, this thickens everything, makes it harder to push through the system, pressure reads higher.
I have a 2002 truck with a 5.3L in it. Swapped from Fram to Wix filter, filled with 5W30 and added a bottle of Lucas. Pressure went from 20 idle/45 on the road to 30 idle/60 on the road. Other than viscosity, Lucas has a ton of additives and helps oil cling rather than being shed as thinner oils are. I'd probably try 30wt with Lucas, your pressures will probably be the same as 40wt.

Through my own wasted time and money using trial and error, I have arrived at a short list of stuff I use on my junk for maintenance, etc.
Trans-X is pretty good, Lucas oil stabilizer is the ****, Wix filters have never let me down and damned near any oil will be just fine as long as it's filtered and changed as it should be. Don't skimp on brake pads - the cheap junk dusts up your wheels and that PITA is enough on its own to step up to better pads.
Most additives are worthless as are most Mickey Mouse devices to help with power, emissions, whatever.
In a room full of superheroes, look for the baddest of the bad, Chuck Norris. Easy to find, he'll be the one NOT wearing leotards. Same with sales ads for all the **** on the market for cars nowadays. If it's good, it doesn't need a flashy package to sell it.
Rant over, Merry Christmas everybody!!!