To put it in plain language
Total Bull Dust
I have TimeCutters, Z-Masters & even Titans in my run & they all easily push, even on grass with the by-pass open .
Your mowers should have HydroGear ZT-2800 transmissions and they should roll freely with the bypass fully open
As suggested before, get under the mower & check that the bypass valve moves all the way to the end of it's travel before the rods you pull get to the lock ring
If necessary remove the bypass rods , and move the lever on the gear box by hand ( they can be a little stiff )
I would almost gurantee that the arm ( lever if you like ) is not moving all the way that it should .
As for what else you can do try writing ( not phoning ) to HydroGear and ask why their units installed on your mower do not roll freely.
You will need the model & serial numbers from the stickers on them .
And the weight of the mower means nothing unless you are pushing up hill.
I had a friend who worked at the Jet base and they used to have "drag races" to see who could pull a 727 the furthest in 2 minutes and a 727 ( even empty ) weighs a lot more than your mower .
I would also write to Toro and ask them if the mower should push freely and tell them exactly what your dealer told you ( name the dealer & the person if you know it ) .
Toro do not tollerate poor customer service and in particular dealers who lie to customers .
When you write to HydroGear & Toro, have the parts book open and use the correct names & part numbers so they know exactly what you are talking about . If you start talking about "pins" your request will get nowhere .