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The first thing to do (unless you are using your 4L80E strictly for towing) is send the stock converter to scrap, as it’s more than 50 pounds and too tight for performance use. Several companies build performance converters. The choice is whether or not to go with a lock-up converter. A lock-up eliminates slippage for long-distance cruising. This reduces fluid temperature and cuts cruise rpm by about 200–300, but lock-up converters are more expensive. The coverter shown here is actually a TCI piece for a TH400.