Ny guess would be, at some time, your batteries may have been undercharged. That would be consistent with the lack of capacity you're experiencing.
Old Guy's rejuvenation charging method may recover a sulfated battery. I've done similar. You really need more than 100 amp charger to make a difference and voltage has to be monitored so plate loss isn't an issue. When I've used the OG method, I flip the charger setting to 200 A but only for a second or two. I'll then back it down to 20A.
Your PD charger should reach 14.4 +V. You want to make sure it does. GC2 batteries really like higher charge voltage. Depending on temps, 14.8V seems to treat them well.