The answer here lies in the fact that transmissions need hydraulic pressure to perform their shifting function. When a filter is clogged, the automatic transmission fluid can not pass from one area to the next, or from the pump to the converter because waste material from the automatic transmission is blocking the passageway. This inconsistency in the flow of oil results in slipping, delayed shifting and thus harder shifting. If the problem is corrected promptly you have a higher probability of not incurring any long lasting damage requiring a transmission repair. We would recommend the replacement of your old backed-up filter, replacement of the old contaminated fluid, and the install of a fresh pan gasket. All this is performed with our Signature $8.88 Transmission Fluid Change. Please see our locations page to find the number for your location in: Katy, Cypress, Spring, The Woodlands, Tomball, Bellaire, Galleria, Sugar Land, Heights, Midtown, Downtown, Missouri City, Stafford, and Pearland.