Need help with understanding PMDC Motors
What I don't understand is how a 12v PMDC 90:1 worm drive motor can be
  rated at 2.3hp. As far as I can tell, it looks to be the same motor
  I'm planning to use, and mine is a 12v 600w 60:1 worm drive that is
  rated at 0.8hp.


200lb * 140ft/min is ~0.85hp or 630W (if motor/gearbox efficiency was 70% then it would need to pull ~900W = 12V x 75A from the battery). If your motor's 600W 0.8hp rating is output power then it may have similar performance.  


  Is the 2.3hp a rating of the actual motor or what is coming off the
  drive shaft?


Maximum output power of a PM DC motor is achieved when it is loaded down to 50% of free-running rpm, at which point it is 50% efficient so only half the input power comes out the shaft while the other half just heats up the motor. The motor could eventually overheat at this power level, so it may be 'de-rated' for continuous operation. 

Horsepower is generally output power, while Watts could be input or output. Without detailed specifications you don't know what the 2.3hp refers to. In this case I suspect it is maximum output power, not continuous duty output.

At lower loading motor speed increases and efficiency improves, typically peaking at 85~90% of no-load rpm. A motor with higher efficiency has less heat to get rid of so it can be run at higher output power. It may also be more compact because it doesn't need as large a surface area to dissipate the heat. 

Obtaining higher efficiency requires the use of more exotic materials (eg. Neodymium magnets, grain-orientated silicon steel) and finer construction (tighter windings, thinner laminations, better bearings etc.) which raises the price. A $1200 package should have a high quality motor in it!   


  3600/90:1 = 40rpm at the drive pulley. 1'(12") x 3.14 x 40rpm = 125.6'
  per minute ....without load. Is this even possible?
  
  Other than the 90:1 gearing, I don't see how they can claim a 140' per
  minute pull of a 200lb weight on a 90:1 ratio of a motor speed of
  3600rpm,with a drive pulley of about 12"


The 90:1 geared motors are rated for up to 120ft/min, and it is not entirely clear whether they can pull 200lb at that speed. For example the 'Power Hauler HD3™ Motor Package' is... 


  Equipped with our powerful 2.3 hp 12 volt powerdrive with our zero
  maintenance 90:1 high torque oil bath worm drive gear box which
  provides pulling speeds up to 120 feet per minute with a 200 lbs. max
  load.


Note they do not say that it can do 120ft/min and 200lbs at the same time - but even if they did it could just be inaccurate paraphrasing of the actual spec.