Re: worn cam?
It could be...
Some aftermarket cams are infamous for wearing out quickly. A lot of them are re-grinds and they tend not to be well-hardened. Some of them also are only engineered for lift and not longevity, so they tend to destroy themselves and the lifters after as little as 10-20k miles. I don't know if you can do this on your engine, but on my Buick V6 I can visually inspect the camshaft and lifters by taking off the intake manifold. (It's easy on my engine, the distributor doesn't pass through it).
Another thought is that your timing chain may have too much slack and the valve timing is sloppy at low rpm's. Put a timing light on it and make sure the timing doesn't jump around at idle (disconnect the vac advance first). If it does jump around, either your chain is bad or your distributor is. Get a vacuum gauge and hook it up to mainifold vacuum. The little pamphlet that comes with it will tell you how to read it. If the vacuum jumps around a lot at idle it is a good indication that something is amiss. With a vacuum gauge you can troubleshoot a bad mixture or a bad cylinder or many bad cylinders, and depending on how the needle moves bad valves/cam or bad rings. My vacuum gauge oscillates a bit at idle and I know from the way my engine behaves that the timing chain is getting sloppy. Buick 225's are notorious for eating them due to their odd firing order. When it gets worse I will tear into it and fix it. I can tell that the water pump wants to spring a leak soon, so when it does I will just do everything.
I hope this helps,
1955 Willys CJ5 Buick 225 V6 160HP 270ft-lbs, T90 trans, Warn OD, PTO winch, Spicer 18 T Case, RS9000's, Dana 25F/ 44R,
5.38:1 gears, 11" brakes, Bestop Supertop, Hurculiner