WP's units were amongst the first built for production and thus  were at the forefront EMD's field "debugging" efforts. Immediate problems experienced were: Traction motor field shunting problems, unreliable high power rectifier diodes, and automatic wheelslip unreliability, which resulted in units not loading when they should. Nonetheless, WP's initial opinion was good: The GP40s were good pullers and EMD was obviously behind the model 100%, making a significant effort to eliminate each problem whenever a bug reared its ugly little head.

WP went back to EMD the following year, taking delivery of an additional six units (3511-3516) in April of 1967, then a third order for ten more in 1970 (3517-3526). 

This third order was the first to be delivered in the new Perlman Green paint and also featured the first GP40 casualty (the 3505) as a trade-in. To increase unit visibility WP also applied red and white oscillating signal lights and installed larger snowplow pilots to each new unit's nose once delivered. 

In 1971 the railroad ordered its final 18 GP40s, delivered in August and September of that year as the 3527-3544. These units came from the factory with nose light package and the now-standard large pilot plow. Additionally, WP upgraded the order to include extended dynamic brakes, a feature not found on earlier examples. 
 

Kyle Brehm Photo, Rattenne Collection

WP 3538  means business as it rolls through the snow at Clear Creek Junction on the High Line.  Part of the last order of  GP40s, the 3538 displays its as-delievered appearance: full headlight package, oversized snowplow and Perlman Green paint scheme with full nose striping.