Take this from someone who has been there. Save your money until you can afford to do it right. Your truck isn't broken just weak. Find out why it is weak first. Do a compression check, check fuel pressure while it is running in the upper rpms where your truck is struggling and under the same load, check the timing, throw a vacuum gauge on it and see if you have 18+" of steady vacuum. Clean your throttle body. So far you have just used tools that if you are around vehicles you should buy anyway. Now spend a couple of bucks to have someone knowledgeable with GM OBD1 red the data stream. A problem now that isn't directly engine related will effect your cam/head swap and just cost you more money that you won't have.
Once you have confirmed that your truck is at 100% then and only then, drop some cash on a Vortec core engine. I will never do a flat tappet cam again if there is an option for a roller. With the removal of ZDDP from the oils of today it is just too easy to wipe a lobe off of a cam. I have always hated a 20-30 minute break in of a cam as well. Just really unnerving even though I know what I'm doing. A roller cam has less friction, will wind quicker and be more efficient/powerful for similar specs. Vortec heads are good but with the cost of heads (and potential machine work) , a manifold, adapter, fluids and gaskets you can easily exceed $500. Someone here will argue that it can be done cheaper and it can but you have you buy good deals which takes time. If you set aside $100-$150 a month you can afford a $200-300 core engine, have the heads rebuilt, have a machine shop check the block, assemble it yourself with basic quality oil pump, rings, bearings and gaskets and do a nice mild cam with the vortec intake. You can build this on a budget in a year or less. Once your engine is ready find a buyer for your current engine because it is worth more running. Take that money and buy the extras for the swap like fluids, belt, new thermostat, hoses and I always do a water pump as well.
That is my 2 cents.