Thanks for the advice. If I decide to go through with this method I would use 23/32 or 3/4 plywood to drill over the shims to level (about every foot), that is supposed to be a safe enough distance to prevent bouncing.

Looking on Zillow the house built next to mine is a single story with a basement. Layouts are similar but their basement is unfinished with several beams spanning across the center. Not sure why the original builders decided to forego it with this one but is probably necessary to prevent future sag.

True. I'll reach back out to him and a few others before I start working on anything. Thank you.

Thank you. I will give the structural engineer another call in a few weeks, hopefully he hasn't retired yet. He built his house in the 70's and had a similar issue (mine was built in '77), but hadn't addressed it at the time.

Adding the beams may be a better permanent fix without having to disturb the flooring. The majority of the bowing is in the hallway (dead center above the garage) and part of the primary bedroom. If that is rectified somewhat with beams across the garage I'd be satisfied until I explore other options after seeing how it holds up after an extended time. Not looking for perfect just better than what it is right now.

Thank you! That is alot to think over. It would be a bit expensive but if it takes me 2-3 weeks and another $2500+ in Hardwood/Subfloor its worth it to me if strengthens the joists and lasts past the life of the replacement flooring.