are the carriage rollers binding up in the channel(do they turn when lifting or just slide up with carriage)? Maybe lube the channels so it rolls more easily. Just had a truck yesterday that did this,the inside of the first stage where the carriage rides was rusty and the carriage rollers were grabbing and pushing the first stage up along with it, used some inner lube(Clark PN# 886396) and greased the inside of the first stage and worked fine.