Look at it this way. It worked when it came off the lot, therefore it has the potential to work that way again. Anything you have done to the vehicle, to include the engine, is suspect, as is everything related to the injection setup.
Not saying you are incompetent, simply that it worked at one point, and now it doesn't. Throwing money at a problem like this rarely works. Sure, putting a new injection system in MIGHT work, but how much is that going to cost you, simply to get around whatever is wrong right now.
You need to change your thought process from assuming that anything works because its new. New means nothing, other than it is untested in use. I will gladly use a known good part over a new one, at least for testing, because I KNOW it works. If your thought process doesn't change, then you will miss potential problems, and never figure out the problem. As well as spend $1500 to fix a $50 problem. So what if the studs are screw in? Not one has ever come off the line flawed? No rockers have ever let a pushrod go through the end of them? No pushrods ever bend? Hydraulic lifters never fail? Your problem may not be hardware. But you need to ELIMINATE problems by actually testing/checking components, not assuming anything. So far that method hasn't worked, right?
Think about it. Even for diagnostics, how much could you buy a complete, running TBI system for just to test? $300? How much could you sell it for when you are done? $300? I think it's an outrageous idea, but if you took a known working injection system off of one vehicle, put it on yours, and the problem disappeared, you'd still be ahead $1200 even if you never sold it. Most everything on the system can be tested, so spares aren't really necessary. If it DIDN'T solve the problem, then your problem is obviously engine related.
