Ford Repair: 87 f-150 spark knock, timing chain replacement, ford f 150

Question
I have a 87 ford f-150 with a 5.0,4 spd,4x4, it has a spark knock, when coming to a small incline about middle was up and about 1500 to 1800 rpm it starts to spark knock.I replaced o2 sensor, replaced egr, check vacuum lines, retard timing a couple degrees, even tried to run 93 octane.Still have a spark knock and lost of power, since I retard the timing alittle, it went away but came back. I do have 33/12.50/15 tires but I've always had these tire size on and never had a problem, that why I retarded the eng. due to the fact it may have a load issue. Your help and advise would be helpful!

Answer
My friend you are about ready for a timing chain.It is probably stretched if it goes away when the timing is adjusted.I cannot say enough about our 302's.How many miles and or last timing chain service?Want my advice,go gear drive....Well worth the money.They are awesome.It's a pretty easy task,of course I am the guy that would throw a mild cam and would mix it up a little bit.A basic timing chain replacement can be done for well under a 100 bucks w/o labor.