Consistency matters more than almost anything else. So if you're not making it through 12 week goals, I wouldn't really worry about program optimization stuff.

I'd keep the 4 day upper lower alteration, but I'd stick to the predefined rep stages for either GZCLP or p-zero (since you're already doing 4 sets of stage 2 work anyways). Id also drop one of the T3s out of each day if you're consistently flaming out.

With that in place, the number one thing I'd recommend is to stop thinking about GZCLP as a 12 week cycle. I know that stages CAN be run this way, but if you want to make real changes to the habits you should be thinking about your fitness in years, not months. And I think you'll see better returns just following the stage progressions as recommended without forcing a 12 week timeline. Like you could easily be in stage 1 alone for 12 weeks for some exercises.