I had an engine built for my 87 K5 and had my friend install it. I had the builders use flat top pistons, a mild cam, mill the heads, and install an Edelbrock Performer intake. My friend who did the install did great. It looks like its all original, which is exactly what I wanted. Now the problem... When the truck is first started, it idles extremely low, almost dying for about 20 seconds. Then the idle picks up and it runs smooth but smells a little rich. It has no power (less than the old 201k mi motor) but will run good for about 5 minutes of driving, then the service engine soon light pops on and the power drops even more to the point that it does not want to accelerate at all and keeping it going 55 is a chore. On one test drive after driving 6 miles, 2 of which the service engine soon light was on, we popped the hood and the passenger side back half of the exhaust manifold was cherry red. The engine code being thrown was a code 43, so the ecm was retarding the timing. I have spoke to numerous mechanics getting answers from a dirt dobber in the exhaust manifold to its running rich, running lean, map sensor is bad, timing is off, but friend says no way on exhaust manifold because he duct taped it up and a hammer all the way up and down the manifold and pipes didnt find anything. A big problem is I am stationed in Virginia and the truck is in TX. I went on leave to drive it up here but obviously I didnt. Any suggestions before I have my dad take it to a mechanic and spend another thousand dollars on it?