So your RW gauge reads 65 psi, then once your torch activates it drops to 45 psi?
That’s definitely not correct, you should only see ~5 psi drop, realistically you want to see 70-75psi on that gauge WHILE cutting.
Is that the only gauge on your system that shows a 20psi drop when it’s activated?
I’d try bumping the internal regulator pressure up, but if you look in the forum I had a similar issue and wound up replacing my internal regulator as I determined it was bad.
I’m not saying it’s your internal regulator, it could be anywhere in your system, you’ll need to trace backwards and eliminate possibilities to find why you’re dropping 20psi. You can basically attach a gauge to a blow gun and attach it to different junctions in your air line setup and when you pull the blow gun trigger you can see if it drops 20 psi or not
Here’s where I ran into the same 20 psi drop issue: Cut Quality Help - #21 by mechanic416
After I replaced my internal regulator it went to just a 5 psi drop which is normal (I also had a separate air supply issue that wound up being another regulator I had put in line for testing that was brand new but would randomly stop flowing air, fun times)