Welcome to the FMCA Forum.
Very difficult for us to "arm chair" diagnose your issue.
My first question is how many miles on it. If 30k plus, have you had the initial valve adjustment?
Has a Caterpillar dealer put it on their computer to check for codes?
As far as starting, is the intake manifold heater working as it should?
When were the fuel filter(s) changed last? Clogged filters can give several different symptoms.
Brett and Dianne Wolfe
2003 Alpine 38'
Moderator, FMCA Forums
Chairman, FMCA Technical Advisory Committee 2011- Present
Member, FMCA Long-Range and Development Committee 2007-2009 and 2014-2015
Moderator, http://www.dieselrvclub.org/(FMCA chapter)