Trying to slow down the speed of the Latham Trim Tabs, up and down. When you hit the tab switch, the tabs move way to fast. First thought was to reduce the size of the fitting going into the pump.

Try thicker oil

Did you ask anyone at Latham?

Called Latham, they want to see pictures of the pump, hoses and tabs. I asked about reducing the fitting size and they said that might be a solution.

had same problem on my 27 excalibur vee ....
being only 5'10" wide at transom and 24 degree bottom,,,
tabs were so fast would jerk boat when trying to level/adjust ,,,just flicking the trim buttons
put on mercury 24volt pump motor on 1 side I had left over from my F1/2 days for the up/down on the 12" champ mid
as that's how merc made the up/down slower than trim/tab pump assembly
and on 12 volts slowed pump way down to be tunable ,,so bought another for other side
and loved small bumps bearly moving rams at higher speeds not drastically changing hull attitude
was originally going to do the restrictor route but the slower turning motor didn't add extra pressure to the pump assembly like a restrictor would do trying to get fluid out pump ,,,,,,
if want to try motors I don't know the mercury p# but the
pro marine p # 6219 and is an arco oildyne replacement pump motor 24v 3 wire ,,,

I like the idea of slowing the pump down
McMaster Carr has flow regulating fittings, but they are not cheap and how do you know where to start with GPM

Had same situation on my avanti... Never figured out why my pumps were so fast? Dangerous on that small boat with big tabs.

Check McMaster carr for a hydraulic flow control valve, it will have a dial knob...

From there you can dial it in ans run them side by side until even.

basically chokes the pump flow until tabs slow. It does makes the pump sound strained, but I never had a issue in 5 seasons?

Good luck.

move the pumps further away and run longer lines .

IMO reducing fitting size will cause higher pressures in which might or down the road cause external oil leaks a lot easier.

I would also try a higher viscosity oil but not too high.

possible look into adjustable proportional flow control valves. Also they can be called flow control valves.

Mine were ridiculously fast , I played with all the settings.. at the end of the day they were drive pumps not trim tab pumps.
once I put in the right pumps all was good.