So hydraulic main slide. OK. Your rams are set too low. As they start to pull in, being that they are attached to the outside edge of the slide and are set too low, they are pulling down as they go in. As the slide pulls in with the rams set too low, the inside most point of the slide will go up needing a hand to pull it down. If you look at the hydraulic gear under the slide, there is a head adjustment on both ends of the slide with two bolts and one set bolt on each. You need to loosen the bolts and raise the heads on both ends equally. This is something a competent dealer should have taken care of correctly the first time...