My Branson 8050 with the power shuttle has a operating pump for the shuttle in the transmission,
the first winter i owned it you could not start it when it was zero F or less it would crank over one revolution and just stop.
Finally figured out that heating the transmission case and hydraulic oil she'd start fine the factory fill would not pump when cold.
My dealer ended up recommending a Gulf synthetic transmission/hydraulic fluid;
331970 Gulf Synthetic® All Season Tractor Fluid,
This fluid meets or exceeds the JD "D", the Case New Holland 3526 and Kubota Super UDT, Super UDT2.
It has a pour point of -58 F.
I ended up using Ce-Pe-Co multi purpose fluid in it,
and it starts every time now, the coldest was -24F one morning it did have the block heater pluged in for a couple of hours,
I did not have a transmission heater at that time on her.