MM500 & SW2500 are identical except for packaging 
GTO PROMighty MuleDatesNotes
GTO Pro100Xpre 1995Discontinued
GTO Pro1000FM7001995-2004 Replaced by SW3000
GTO Pro 1800Xpre 1995-1997Discontinued
GTO Pro 2000X1997-2004Replaced by SW4000
GTO Pro SW1500MM3502005-SW1500 Discontinued
GTO Pro SW2500MM5002005- 
GTO Pro SW3000X2004-2006Upgraded to XL
GTO Pro SW4000X2004-2006Upgraded to XL
GTO Pro SW3000XLX2006-2010 
GTO Pro SW4000XLX2006- 
GTO Pro SW2000XLX2007-Pro Economy model
XMM2002008-MM Super Light Duty
Brand Differences
Both Mighty Mule, E-Z Gate Opener brands and GTO PRO Professional Access Systems brands are made by the same company, GTO LLC. Basically Mighty Mule economy openers were created for consumer installation and GTO PRO for professional dealer installation. However, some items are branded both ways depending on the distribution path. GTO PRO Professional Access Systems also offers additional Long Lasting Heavier Models for heavy duty residential and commercial applications.
As of late, many consumers are opting for the heavier GTO PRO Units even though they plan to install them themselves.

While Mighty Mule was intended for retailers and GTO For Professional Dealers, there is some crossing of the lines. Generally, Professional Dealers usually recommend the sturdier units. 
 GTO Gate Openers & Accessories 
Don't be afraid to use a unit with a heavier rating in order to get more durability.
March of 2000: 1000 & 2000 upgraded to new UL325 specs. UL325 recommends specific safety standards for gate operator systems. All systems manufactured since March of 2000 are UL325 complient.
 GTO Factory Authorized Dealer 
 Mighty Mule Factory Authorized Dealer 
 Mighty Mule Gate Openers & Accessories 
The GTO - Mighty Mule Difference
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