1990 GMC Jimmy California smog

I have a 90 Gmc Jimmy. It has the 5.7 with tbi. The motor was replaced and actually has about 90,000 miles on it. I recently went in for my biannual smog inspection. It passed with flying colors two years ago so I really didn't do anything to it before the first inspection seeing how it runs great. Well, of course, it failed. It only failed HC's at idle (170ppm) though. 120ppm is passing where I live. Everything else came in way under specs and even the HC's went down to 53 at 2500 rpm. I took her home and did the tune up. Changed the plugs, wires, cap and rotor, fuel and air filters, changed the oil, Ran a bottle of Lucas injection system cleaner through with a quarter tank of Chevron regular. Took it for a long drive before the second test and really hammered it pretty good to blow it out a little since I live close to work and normally only drive a few miles at a time. It failed again even though the HC's came down to 140. I'm only 20 ppm off. The inspector old me the idle was a bit high. It was at 1070 rpm this time, and when it passed 2 years ago it was at 1025rpm. I've checked for leaks around the throttle body gasket, checked for vacuum leaks and checked the EGR. I'm gonna throw an oxygen sensor at it and see if it seems to run any better. The only other thing I can think of is the Cat but I really don't want to blow the money on it when I'm so close, but I really don't know when it was changed last since I've only owned the truck for about three years. This truck runs really good though it is a bit sluggish off the line. Never stalls, misses, or anything else. Please any help would be much appreciated. Thanks.