According to Stuart Benoff :

The pump is sending water to the wall outlet and then the cleaner is
attached to the wall. The 14-15 PSI reading is from the wall outlet
without the cleaner attached.

Is the wall outlet free flowing or plugged?

When I take the measurement from the end
of the hose that attaches to the cleaner it's at 11 PSI.

Same question.

The hose is a 5/8" hose and is about 22 feet long.

I think you need to connect the cleaner to the line and then
measure pressure, at both ends. The drop from 14-15 to 11
seems a bit high, suggesting the hose is undersized.

5/8" garden hose? Use 3/4" high quality hose. Some 5/8"
hoses are quite flow restricted, especially those with cheap
end fittings. This could be your problem right there.

The pump is a Magnetek 1081 PB4 Booster Pump, 3/4 hp, 3450 rpm - part
#173840-20 but I can't find the specs for it online.

3/4HP Magneteks appears to be one of the pumps of choice for pool
cleaners according to the number of hits on Google. Eg: they're
bundled with Polaris and other units.

So it should be working with yours.

I also did as you suggested and called the manufacturer of the cleaner.
Their 3/4 hp pump is capable of 67-80 GPM

67-80GPM at 20PSI? Good grief, that's _high_ for a 3/4HP unit. I'd
expect a pump delivering that performance to be 2HP or more.

You simply _cannot_ push 67 GPM thru even 3/4" copper pipe with any
sort of efficiency, the friction losses are _enormous_[+]. 13 GPM is
more like an acceptable upper limit thru pipe that size. 1/2" pipe
is around 8 GPM max, and garden hose (smaller "real" diameter compared
to nominal inside diameter) will be less. Especially since
some cheap garden hose has very restrictive hose fittings. Watch
out for restrictive valves too (if there are any valves in the line).
Use full aperture ball or gate valves. Washer type stop valves
are quite flow restrictive.

Are you sure they didn't say 6.7-8.0 GPM? _That_ is reasonable,
and suggests that the hose (if you supplied it) is likely at fault.

[+] There is a "practical speed limit" for efficient pushing of
water through pipe, above it, the friction loss becomes ridiculously
high. With 3/4" copper/PVC, that "speed limit" is achieved at roughly
13-15GPM. Trying to exceed 13-15GPM in 3/4" pipe means that you have
to size the pump FAR larger than necessary (and thus waste a lot
of money) to get the device to work. If you don't size the pump
that large, the device simply doesn't get the water volume it needs.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.