UPDATE:
Ok, we pulled out the cartridges and closed the filter back up and powered it on again to see if we had bad cartridges -- STILL no pull AT ALL.

Then, we carefully removed the housing around the impeller (I tried to reach into it with my fingers, but my hand was too large for the opening). I really believed that it could be a clogged impeller -- it made perfect sense! -- but it was totally clear!

So, I guess I am looking at a new pump. I have seen several models that are comparable, price-wise, but I don't know the reputations of these brands.
Do any of you have an opinion or preference between these:

* HAYWARD 1 HP NORTHSTAR SWIMMING POOL PUMP SP4007X10NS
* Waterway Champion 1 HP CHAMPS-110
* Hayward Super Pump 1 HP ( #SP2607X10)
* Pentair Super Flo 1 HP Pool Pump
OR can you suggest another one????