Opening up the gas port is very easy.
Get a set of numbered drill bits from 31-40.
Get a 1/4" brass rod to protect the bore.
Start small, use lots of cutting fluid.
Use the correct speed for drilling steel.
If you break off a bit and it does not stick into the barrel, go to the range and shoot it out.
Do NOT go bigger than .120" with a 16" barrel, if you have to somthing else is wrong.
I go strait to 7/64" (.109) for my para lenght (17.375") barrels.
If you can get reamers the correct size that is much better.
I test at the range with a couple of different loads, and try to have the action work well with the lightest load when the gas adjustment ring is at "3".
Have you checked the recoil spring tube? Sometimes heavy grease will cause the action to be really slugish. Did you use the same gas block? After they wear out the gas tube needs to be soldered in