What does your contract say? What is the GC doing to make sure the subs get the work done?

If you are self GC'ing all you can do is beg, possibly offer an incentive ($$) or wait. If you are self GC'ing this is part of the pit falls of why a one time HO/GC does not always equate to a savings.

Sounds like you are GC'ing it yourself. Millworkman is exactly correct and I've been in those positions NUMEROUS times. You are NOT important to the sub because you are what I call a "one and doner." He has to keep his bread and butter customers happy (i.e., the GC's that send him the bulk of his business).

The only recourse you have is to find another sub, but, in most locations, those are hard to come by these days. You're just gonna have to grow in patience. GC'ing it yourself is why it can take over a year+ to complete a house from ground break to move in and why a GC can get you moved in in half the time. Ask me how I know ;)

Ha ya I thought the drywall step would be easy since they shouldn’t need much handholding and that I’d be able to focus on other stuff. Hahahahaaaa

Oh noooo, the drywall is always one of the most excruciating steps in home building. I've never had a painless experience with it and we've built and/or remodeled several times.

DIY?

Communicate daily with this guy. Be the first or the last one he hears from daily. You should be in the rotation and he should be able to tell you how many days out for each step.

Call or text, and back up with an email. Sometimes arrival at their office/shop can be effective.

You may have overpaid the phase or not, but he is likely busy with GCs who call & pay early and often with lots of work.

The contract clause is "force majeure" for labor shortages.

Make sure the project is always ready. Heat for drywall finishing/taping, water & power available, etc. Trades will string you out when you're not ready or are still making decisions and changes. If they arrive and the job is not ready, they may move on to another project and may not return for weeks even if you're ready 4 hours later.

I would approach the discussion from the view that he is an honest guy who wants to do a good job but he is overextended. He may have had labor trouble, perhaps has some workers who quit or are temporarily out of commission. As a one time, low priority customer finishing up this contract is low priority for him from a business perspective. Your approach has to come from the flattery side of what a good, hardworking guy he is and how you know he is trying not to ignore your project even though he is overwhelmed.

You need to have a serious conversation with him as both you and he would like to get your project done and off his to-do list. Ask him how he plans to handle your job. Ask him what assistance could you offer to help him complete the project sooner. I have found that people usually do a better job following the plan they developed rather than a plan imposed on them by some outside project manager. Offer some extra money to pay overtime for his guys so he can work some long days to make some good progress. Offer to help move materials, do cleanup, run errands, make coffee and provide something to make it is a desirable site. Donuts, sandwiches, candy bars, soda...any of those are cheaper than paying another day of utilities, property taxes and carrying costs on a stalled project.

If you are going to DIY build, you need to frame your approach and thinking to one of being a problem solver. All successful builders & their project managers learn pointing fingers and playing the blame game never moves the project forward. Many times "righting a wrong"just doesn't make sense in the overall outcome of the project.

Great problem solving strategies have been mentioned, have your job site ready to go, make decisions quickly (no back/forth 10 phone calls & 50 emails to discuss how many shades of blue there is), incentive pay for early finish or working longer to get your job done, and DO NOT haggle over pennies to price quotes already agreed too, even if one believes they received one less 2x4 than what they were expecting (keeping end goal in mind will help let that 2x4 not become a "hill to die on").

Trying to pay less AFTER work is already complete, combined with too much discussion to get to a decision, are the top reasons why most subs that work new construction do not like to work directly with homeowners or DIY, many outright refuse too, or will only take your job as extra "fill in" work. Is it right? No, but it's reality thanks to prominent attitudes for decades that trades are "beneath us" leading to a dwindling, aging work force.

A recent quote on houzz referred to subs as "know nothing grunts". As a DIY project manager, this approach and mind set is doomed to a rough road. Greater success will be had focusing on the end game, and one day you will wake up to a finished home, although the time to complete will likely not mirror a builder project. Good luck on your home.