GMC Repair: 89 GMC 5.7, fuel pressure gauge, vacuum leaks

Question
Truck turns over too long before starting after sitting for a few hours (starts good if only off for a short time)then idles too fast for first 15 mins. of driving regardless of temp. outside. Occasional code 43 and sluggish but goes away after shut off. New temp switch, IAC valve, distributor (from wreckers) fuel filter and cat converter. If leakdown is occuring, how do I check?

Answer
Hi
For fuel leakdown, You'll need to hook a fuel pressure gauge to the fuel system, usually hook where the filter would be. should be 9-13 psi running and should not leak down fast, if at all.
Code 43 is ESC circuit. Check your knock sensors , single wire sensors located on block, one is right in front of starter, other is opposite side of block, same place.
Does the engine knock when it idles high? If so the system is functioning normally and the knock should be addressed.
The ESC module is mounted USUALLY on the right side (passanger side) valve cover. It COULD be faulty, although I have NEVER replaced one in almost 20 years of GM service.
Check for Vacuum leaks, especially around the Throttle Body gasket, and the intake manifold gaskets. You may have a leak that after it heats up, the "gap" closes and vacuum cannot escape.
Check these items.
If you need more help, either follow up a post, or take it to a local repair shop, and get them to diagnose it. Tell them what has been done and what you have checked.
I hope this helps.
Just advice from experience.
Good Luck
Pawl