37 lbs in 4 months at 64 on 3.5mg is genuinely strong progress - the pace is faster than most people see at that starting weight and age. The next 28 lbs to target tends to come more gradually as you get closer, which is the normal pattern; the rate slows but doesn't stop.
Protein tracking at this stage matters more than it did early on - the lower appetite makes it easy to miss the intake that protects lean mass at 64. Most men in this range find 140-160g/day needs active effort to hit when appetite is suppressed. The 3.5mg staying effective without needing bumps is a good sign.