Kenmore 80 Series spins intermittently or weakly

From reading several threads, I think I know what the problem is, but I want to make sure.

For several months or more, our washer would not complete the spin cycle. We would never witness, just the pile of soaked laundry in the machine after the cycle was through. It seems like it only happened with the Ultra Clean cycle and possibly only with heavy loads. I know that there might be an imbalance shutoff, but it used to not do this. Now it seems like the spin cycle is getting weak. I'm thinking the following from other threads,

1) The timer if it is only happening during one cycle
2) The coupler
3) The clutch

If it is the coupler, how can I tell if it is bad rather than replacing it and seeing if it works? I hate to throw away the money.

Same goes for the clutch, how can I tell if it is bad before I replace it. Again I hate to waste money on a part and shipping and possibly not be able to return it. To replace the clutch, do I need to remove the agitator first and then drop the motor from below?

Thanks,
Alex