6.5 hard starting & no power.
 

I have a stock 96 GMC 6.5 turbo 1/2 ton that I parked last fall for the winter. It was running fine then. Tried to start it when it was still freezing out and it would crank a long time before firing a bit but wouldn't start. Dragged it inside to warm it up and after lots of cranking it would start but could only get it up to 30 or 40 mph. Engine seemed to run fine just a very spongy pedal. I changed the fuel filter and the lift pump with no change. Found another PMD and plugged it in, drove around the block and nothing changed. I disconnected the connectors around the PMD and behind the fuel filter and sprayed them with brake clean. Still slow starting and no power, but I am getting it up to 50 55 mph now. Ambient temperature has warmed up to well above freezing so not sure if that accounts for the slight improvement. Couple other things I noticed, glow plugs don't seem to stay on as long as they used to especially after warmed up, and I sometimes get a water in the fuel light intermittently. Cracked the fuel filter petcock a couple times but it doesn't seem to stop it. Water in fuel light is not on when first started. I have had an unrelated check engine code on for months and my code reader walked away over the winter so not sure if there are any new codes. Any ideas where to check next?