K3500 severe lack of power

So I purchased a 99 K3500 crew cab long bed dually a couple weeks ago. While I’m familiar with GM vehicles, this truck is a completely different animal to me. It has 130k on the clock with a 454 L29. Has an occasional hard start issue and has a severe lack of power. I mean, it barely wants to get out of its own way. I put new plugs and wires on it, have a cap and rotor on the way that should be here in a day or 2. I also have a fuel filter waiting for me to get some time to put it on. I purchased it, had it towed home because the wheel cylinders went. I know it’s been sitting since early September 2020. I don’t know how long it’s been sitting before that. The body and frame are in really good shape for being a Pennsylvania truck. So the last time I drove it, right around 1,000-1500 rpm it’ll stumble and then pick up but barely wants to climb a slight grade about a 1/2 mile long at 35 mph. I’m hoping it’s just a clogged fuel filter. I plan on keeping this truck and fixing all the little issues with it. Any help is greatly appreciated.

Also forgot to mention it’s been running hot. Never got above 220-230. It warms up under throttle but if you let it idle it slowly goes down to about 195 or so

Have you pulled any codes to include a transmission code reader?

Only code that came up was for knock sensor 1 that was replaced the next day

Apparently there was a second knock sensor, the wire was burnt off so I spent a day and a half researching which wire it was, found it and replaced the knock sensor. All is well now