If you want to stay in the lift truck trade you will have to have the trade certification eventually. If lift truck courses are not happening try heavy equipment, a lot of the material covered is the same. With 6 years in the trade you should be able to write the test anyway. My suggestion is to specialize in electrical trucks/components (easier/lighter work requiring more brain power/less brawn). If you switch employer make sure that future training is not an empty promise. Talk with techs and check turn over rates. If people leave after a few years it means a poor workplace. Try Sandford College in Lindsay, Ontario, they run short intensive semesters if you want theory knowledge. Good luck.

P.S. For Dan M.
Jess W is a Technician, (capital T not a mistake), the person that gets blamed for operator mistakes, salesman selling whatever was in the yard, and gets grief from the manager because an arbitrary financial target wasn't reached. He is not looking for operator training and can probably teach most trainers a thing or two.