I was in a similar spot a month or 2 ago. '88 k1500 5.7 with coolant issues around the intake or head gaskets. I did some research with the same thoughts- 'if I've got to pull the heads, might was well upgrade them.' From there it is a slippery slope. "New heads? Might as well do the cam while its apart..." Next thing you know a $1,000 repair turned into $3,500 in parts and at least 50 hours of labor (at my speed).
I talked to my machine shop guys about the heads before I tore down the engine. They've been around 25+ years. What they said is the factory castings on these heads aren't great. They're too thin in spots and are prone to cracking. They offered to vat them and pressure test them for cracks. They said there are replacements for these for about $300/per that fix the casting problems and said if I'm not going with an aluminum head its better to replace them with the upgraded cast ones than rework the originals. They said they'd source the replacement heads, test them etc... before I put them it, which makes sense to me. I asked about porting and polishing. Not a bad idea but no one around me does it anymore and it doesn't add that much performance wise. Plus it bills per hour and the time it takes ends up making aluminum heads a better option price wise.
I looked at the summit heads which are no longer being made. I believe they were produced for Summit by someone else that does have TBI heads in stock which flow better with bigger valves. I'll edit this comment when I find my link to those heads. I found a few articles comparing performance of different aftermarket heads on these engines. Although the Edlebrock performer TBI heads are still in production for around $1,100 each, they didn't rate as well as the others in those articles that cost half as much or less. Seems like some of the other performance houses have their own heads too, Jegs and Speedway maybe, and they did well in the test. I didn't get as far as checking those.
In the end, it turned out to be my intake gasket and valve seals. My truck now runs great, has plenty of power for everything I do with it. I'm still planning what I'll do for performance. It'll be heads and a roller cam & rockers, larger injectors, factory intake and a chip I can tune. Mine isn't a daily driver so I can fiddle with it for as long as it takes to get it running right. If you are going to keep the original intake, I suggest replacing the heater quick connect on the intake with either the Dorman stainless one or eliminating it and putting in a nipple. I put in the $12 Dorman steelie rather than replacing the hard pipe and was thankful the pot metal OEM one came out easily.
There is a thread here on performance upgrades which talks about both the TBI and Vortec that is worth a read. Basically for the TBI's it says the first stop has to be the exhaust. It is too restrictive for the CFM produced by the factory engine and any upgrade to the heads and cam produce more CFM. Shorties, a mandrel bent Y-pipe and a high flow cat; or, shorties, dual pipes to a single cat and single muffler (or two cats and two mufflers), all help. It seems like with just shorties, y pipe and cat someone got an extra 50 ponies.
Copied and pasted this from another site tons of awsome info I’ve been on the forum long enough to notice the same questions popping up again and again. Although the forum has a search feature, it is often easier to just ask your question. That's what the forum is for. Well to lessen repeat...
www.gmt400.com
Tranny wise, I put in a corvette servo in the 700R4 and noticed a difference especially in the 2-3 flaring which is all but gone now. For about $50 and some fluid, it was an hour well spent. I'll eventually add the Sonnax 4th gear super hold servo. Next time I'll just get both the 2nd and 4th gear servos from Sonnax and use the factory pin. The 700R4 has some issues that can be fixed with some parts in the valve body. I'm not a tranny guy so I asked here and got some good info that I haven't followed up on yet. I live in the mountains and do some towing so I want to be able to hold gears going downhill to engine brake and am leaning towards the command shift kit plus the stuff to resolve the known issues.
https://www.gmt400.com/threads/700r4-4x4-advice.63915/#post-1346505 My tranny only has 60k miles on it. Otherwise I'd have it rebuilt and get the upgrades done then.