Lately I've noticed a very slight amount of slippage when I use a lot of force pedaling (i.e. starting from a complete stand still). This usually happens right after using a bit of force back-pedaling.

I assumed it was a simple case of a loose cog or lockring (note: these are brand new albeit rather inexpensive). I checked both (with the proper tools--chainwhip and lockring wrench) and they seemed fine. Then I checked the chainring bolts which needed a bit of tightening. All to no avail--the slipping is still there.

My next thought is to replace the chain as it's pretty old, anyway. Or could it be a stripped hub?

Any ideas?

Thanks.