Hello again all, I have a 1978 K5 w/350. It didn't have a timing tab on it. I've had to give it a tune up etc and of course setting the timing was on the list. I had to put a tab on and it seems to me to be in the logical location (kidjethro thought it was in the right spot as well) but now the truck doesn't run right. The numbers given to me were to set it at 4 BTDC. When it is set there I get a strange "bwap" sound out of the exhaust and a hesitation on acceleration. I saw a post by HarryH3 today saying that GM has used two locations for the tab and I was wondering if anyone knew if mine is set up correctly. TDC on the tab is at about 2 o'clock. I can get pics if needed. Once again, thanks for your help all.