Cat 215 Hydraulics Weak after 30 mins

Hello all, First time posting but have been appreciating the forum's knowledge for a few years now. I have new equipment and old, would prefer the older mechanical stuff hands down any day of the week! Spring of 2023 I purchased a 1984 Cat 215 excavator. Serial Number 95Z00796-12Z06465 I am an arborist and primarily use this machine on lot clearing jobs, to keep our shop/log yard organized, and to feed our horizontal grinder. It runs great, fires right up, and is even pretty clean overall. This machine has the three hydraulic pump set up. I serviced all filters when I purchased. Hydraulic fluid has normal color/smell so I did not change that. Mechanical Cat engine. It is very strong when you start the machine and operate for 30 minutes to an hour depending on ambient temperature here in Asheville, NC. Yesterday it was 17 degrees outside. The machine fired right up with a little extra juice to the batteries and operated over an hour and a half before any noticeable drop in power. In 80 degree weather its's much closer to the 30 min mark. This summer I sent the machine to the Cat dealer (just because I had to teach myself that lesson ). For way too much money they did some work to the final drive, water pump, belts, etc. They also tested hydraulic pressure. I don't believe they took the time to properly warm the machine as I had requested. But anyhow, the machine shows pressures were at 100% factory maximums. I've tried to get three separate mechanics to look at the machine, one of which was referred to me as a guy who specializes in this older equipment. They are all either booked months out(which is pretty common for most industries in our area) or keep postponing the initial service visit. I am certainly no expert but I do possess a basic knowledge of hydraulic systems and have a hydraulic test gauge kit that I'm not afraid to get dirty. As I said, the machine runs awesome until it has been operating for quite some time. Factory gauges appear to work and show normal temperatures on everything. The weird thing to me is that all controls seem to lose power at the same time instead of only some which would indicate one bad hydraulic pump. It will still move the booms slowly with minimal weight capacity. The tracks will move the machine on flat ground but won't pull the machine up even the slightest incline. The engine will bog down at this point if you keep pressure on the controls but does not stall. Any help would be greatly appreciated! Thank you in advance for sharing your wisdom.