Room slide out stops and starts

Look on the negative side,.....it may run thru safety switches before going to the pump.
But maybe not on a trailer.

Don't see anything that looks like a breaker/fuse between the battery and the pump.

The positive cable runs to some studs before going to the battery, but this is where other wires are split off from as well (landing gear etc). The wires are just bolted together. The negative wire goes up into the trailer.

Within the trailer there is an automotive 20A fuse (not self resetting) listed as Slide, although this is likely for the outlets/lights but this fuse is fine.

Locate the DC Circuit Breaker on POS wire coming from battery that goes to slides

It will be close to battery.
It is an auto reset....trips/resets
Bad connections (2 studs.power in/power out)
Undersized.

I did check the voltage, it is about 13.5v without running and runs just over 12v when the pump runs.

When the slides stop the voltage drops to 0v and then comes right back up and the slides start moving again.

Any recommendations on what I can try next to isolate this problem?

Check the 12 volt wiring at the HYd pump motor and make sure the cables are tight. Check the wiring from the Pump motor to its source both neg and Pos. Also, have someone operated the slides and take a 12 volt measurement AT the hyd motor and see if the voltage drops below 12 volts when running. Some Hyd and electric slides use a auto reset 12 volt breaker. If bad or loose connection they will trip and reset within a few seconds. If this has happened since new, they may have installed the wrong size breaker for the slide system. Doug