TurboTax says my pension income is $5500 more than the total on theT4A forms (including CPP) that I downloaded from the CRA. What other pensions might I have w/o slips?.

Have you reported foreign pension, or received split pension amounts as transferee?

So far as I know, no to both questions. My only pensions are CPP and my former employer's, which is split into two portions, but both are reported in T4As.

Thanks, I will give that a try.

Can only suggest you edit out /zero out all the downloaded entries from AFR and renter your amounts manually from the T-slips you have received
It's also possible AFR has downloaded a duplicated or invalid slip from the CRA database.
Check all the T4A and T4A(P) entries carefully.