ETS,

1. What you or your customer needs to is to go back to the supplier of the old trucks and get a fuel consumption charger on teh "older" trucks and get the same on the new models.

2. Secondly not all LPG fuel is the same. LP fuel can be either butane or propane or a mixture of both - butane has a signifcant higher heating value rating (BTUs) than propane or will generate more power. It may be possible that the LPG supplier has made a change based on price, availablity, etc

3. What ever the effects of the new EPA lift trucks emissions standards maybe the lift trucks manufactures had to comply with these standards -some manufactuers made complete engine changes to do so. Engine back pressure is not always a bad thing - all engines need to have a bit of back pressure to assure acceptable life - unless they run the NASCAR or Dandy Don Garlits circuit.