Hi Ken,
GPM and PSI are two distinct measurements. Also, the GPM on the label will change with the spray tip being used, therefore, simply measuring the output and basing the results against the label will yield significantly less than 1.4GPM. To put 1.4gpm into perspective, at that rate, the 3 gallons in the Fivestar would be gone in 2 minutes. The actual GPM will be lower than that.
You mentioned you have a 45PSI pump- currently our pumps are 80PSI so I assume this is an older pump- possibly in need of a rebuild.
As Ray Burnfield mentioned, self contained units are lower pressure as the brush is the main agitator. It's possible your problem is not the pump but rather the vacuum. Your pump may be putting down plenty of water but without the vac pulling it out at a noticeable rate, you simply would not know it.
To eliminate the vacuum try the following:
If you're standing behind the machine, remove the vacuum hose cuff on the RIGHT side of the dome and place your hand over the orifice on the dome.
Good suction? The problem is from the vacuum shoe to that hose where it meets the dome. There is either a clog or leak.
Bad suction? Check the air filter on the left hand side of the dome.
Depending on the age of the unit, the filter will either have a hose clamp or be a pull out cartridge. The clamp is the identifier.
Clamp? undo the clamp and pull filter off for cleaning.
No clamp? Standing behind the machine, remove the hose cuff on the LEFT of the dome and pull out cartridge filter and clean.
Check your vacuum shoe to make sure it is even throughout where it makes contact with the floor. Any cracks? Obstructions?
If after these steps you see no change (assuming you checked for clogs), then the vacuum system can be eliminated as the cause of the issue.
You have my info- feel free to call me and we can try some other troubleshooting ideas.
Have a great weekend!