First check after triple-checking for unloaded is slide home, hammer back, thumb safety off, then press down on the chamber area of the barrel with your thumb. Try to push the barrel straight down toward the trigger opening in the frame. Putting the frame in a vise may help you see exactly how much movement there is, and there should be very little. There also should be very little slide to frame movement if you squeeze the slide down hard against the frame. While checking for slack, peer into the muzzle with a pen light and observe if the firing pin is centered in relationship to the chamber. These checks will determine if your slide to frame and barrel to slide and barrel to slide stop relationships are correct. You should also check to make sure the barrel bushing has the correct relief to allow the barrel lugs to fully engage the slide lugs, check that with the slide off the frame and the barrel installed, measure the distance between top of slide and barrel hood with a depth mic while fully engaged and compare to how it measures with the pistol together and in battery. When the slide is off and upside-down, the barrel should "clink" all the way into battery and not be held up by the barrel bushing. If the lugs don't fall all the way into engagement with gravity and you can push the barrel further into lockup against the spring of bushing flex, the bushing needs to be relieved very slightly. If there is an uneven wear pattern on the barrel from the bushing it's also an indicator of a binding condition. While you have the slide off, upside down, and barrel nesting in battery, twist the barrel back and forth to check for excess side-play within the slide, there should be almost none in a match pistol and will probably be a huge amount with a "drop-in" or production barrel. Look in the muzzle again to see if the firing pin hole lines up laterally with the chamber.
Headspace is another thing to check with the slide off, I'm sure you went through this process if fitting a "drop-in" barrel because the only surface with enough meat to file on will be the very back of the barrel hood where it rides the breech face. Basically there should be an absolute minimum of slack between the breech face and barrel hood when the barrel is locked up, essentially the barrel should be snug against the slide when in battery with no fore-aft movement at all.
An important and often overlooked consideration when checking all the things that interface in a 1911 is the function of the barrel link, which is only one thing: It forces the barrel to "rotate" down and out of battery as the slide comes back, that's it. The feature of rotating BACK into battery is controlled by the ramp on the barrel feet and slide stop pin and there should be no stress on the link at all except when unlocking.