SierraMike

Thankfully ( and embarrassingly ) it seems to have been a loose positive connection at the battery. Its a stupid side terminal one and I've stripped the lead threads in the past so I guess this time i didn't tighten it enough. Very grateful for your help and time, I've learned a lot, hopefully I can repay the favor by trying to help someone else in need. Cheers!

That's great food for thought. Interesting development today, doesn't want to hold idle and stalls. Also the clock resets to 1:00. So after it fires I hold the throttle a bit to keep it going and then start driving and it bogs out when the throttle is pressed. After a short distance it seems to move past the problem and throttle response returns to normal.....

I know I have a bad o2 sensor but I cant get it out as its rusted in. Someone else has suggested a leaking injector as well although I don't understand why the truck would fire right up in the morning if a cylinder was full of fuel. Plus I would think the fuel would get past the piston ring overnight and increase the oil level. I did wonder if it's an intake issue as well, I pulled the air box off the throttle body and everything looked fine. I guess I will have to pick a place to start, throw parts at it and just eliminate the possibilities one at a time. You've been a great help, thank you for sharing your knowledge.

I think you may be right, she has 167,000 miles and I've put half that on myself so maybe cap and rotor, plugs and wires wouldn't hurt. Last few days its been cooler and the truck seems to want to start in the afternoon a little easier. Not sure why ambient temperature would play a roll. Anyways thanks for the advice

Not totally sure, fuel pressure is about 55 psi which is a little low I think. I guess probably fuel pump eh? Or check valve? Thanks for responding btw.

So my 1998 Sierra 5.7 started having ignition issues. First start of the day it fires right up. After work in the afternoon and first crank it tries to catch but then just cranks and won't catch. After multiple attempts it will eventually start. I'm roaming the internet for ideas, any help would be greatly appreciated. Thanks for reading. Mike