i have a 98 sierra 3500. 6.5l 85k miles. when i first bought the truck i was having typical pmd problems. so replaced the lift pump and pmd as well as remounted it to the bumber. truck ran great for about 2 or 3 thousand miles. and then started having the same issues. she finally died on me at an intersection and would not start even after a day of letting her cool down. towed her. bought a new pmd and upgraded cooling fins. turned on immidiately and ran good for maybe 30 seconds. started coughing and eventually died but starts right back up and repeats the process every time. if i start it and keep rpms up shell stay running but coughing the whole time. i let it sit for about 2 weeks and came back to check for a clog in the intake and now wont even turn on. extra notes: my air conditioning stopped working a couple weeks before the intersection mishap. and when keeping the rpms up to keep it running i can hear the air pump working harder than usual. any ideas on the matter would be greatly appricated. thank you