I have an 04.5 5.9l 325hp that is having long starts, especially once it's hot.

So a little background, truck belonged to my dad before he passed last year and had mostly sat for the last 3-4 years as he couldn't drive. Since getting it back on the road a few months ago I've done oil change, fuel filter, air filter, crankcase vent filter, crankcase vent oil return line, turbo(stock replacement with 64 mm compressor) and wastegate solenoid. Turbo was losing a bearing and the wiring on the solenoid failed when moving it to the new turbo. Crankcase vent started throwing oil out the vent line, after that was replaced the check valve in the return was still partially plugged so I replaced the line. 246k miles currently on it.

It was starting great when I picked it up, but has gotten worse recently, especially with the high temperatures(95-107) where I live. Once it starts it runs perfect, smooth and steady at ~750 RPM at idle. Strong enough to pull 5% grades at 70 miles an hour with 6500 lbs behind it last weekend. Fuel rail pressure is around 7k at idle and very quickly climbs to 17-18k psi on throttle, peaking around 20k. I have been seeing some high idle at temp after driving, ~950-1000 RPM a few times then it does back to normal after a minute or so. First starts when it's "cold" are relatively quick, but still slower than they were.

I'm not a diesel expert, so am I right in thinking that the place to start is injectors? The numbers lean towards the CP working fine, but weak injectors on startup maybe? Is there a way to test without having to remove the valve cover? Are there other places I should look first? Any tips or tricks if I do need to do injectors?