Pump

Keep in mind that water flow rate, like electrical current, up to the limits of the source is demand based. If a tap is only partially opened, the flow rate will be low, regardless of the capabilities of the pump. If the fully opened flow rate at the tap is still below the pump's capability, a larger pump will not change that. Nor will it raise the water pressure at the tap for a given flow rate.

The higher the flow, the faster the fresh water tank empties and the faster the waste tanks fill.

Quote:
is extremely loud and hardly gives any volume at the taps.
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From that description, the problem is not the pump. You must have a clogged inlet filter.
Even the 1.8 to 2.0 pumps give decent volume at the faucets,
Loud,.....learn to live w/ it. It can be improved a little, but it can't be stopped.

I've got one of the Flojet Sensor VSD pumps. I love it.

Shurflo 4048 pump.........4 gpm/55# discharge pressure LINK

Your faucets are limited to 2.2GPM at 60PSI by EPA regs, so increasing the supply lines likely won't help. Shurflo and Aquajet both make higher volume pumps, with Shurflo's "Revolution" pump getting pretty good marks from many users. To quiet the pump, add a foot or so of soft flexible hose (with a suitable PSI rating) to both the inlet and outlet sides of the pump to minimize the transmission of the pump noise and vibration. Note the loops in the upper part of the photo below taken when I relocated my pump from the bedroom to the wet bay. We hear a low hum from the pump only when things are very quiet.

Generally water line size is not an issue. Pump volume is your problem. There are several pumps on the market that claim to produce 4+ GPM. Pick one and install it. Just dont expect water flow or pressure like at home. No matter which one you choose it will still be set to about 40 PSI