text: In 1982, the coupe and station wagon were discontinued and Canada's Plymouth version of the Diplomat came south of the border. The Plymouth Caravelle was offered in the United States as the Plymouth Gran Fury. 1983 was the last year for the Slant Six, and afterwards, the only available engine was the 318-cid V8 with a two-barrel carburetor. A four-barrel 318 remained the optional engine choice for the police package. For 1984, the appearance of the upscale Special Edition or SE used the Fifth Avenue's front end with its parking lights located above the headlights, and a bright metal cross overlaid on the Chrysler grille's thin vertical bars.  The SE had more exterior trim and an interior that placed the SE between the Diplomat Salon and the Chrysler Fifth Avenue.
  As the 1980s progressed, fewer private customers purchased the Diplomat, and the M-body was eventually dropped during the 1989 model year. Sales of cars equipped with the Police Package represented about half of the Diplomat production after the discontinuation of the coupe and station wagons. Late in the Diplomat's run, the car was subject to the federal "Gas Guzzler Tax" and required premium unleaded gasoline. Although sales were strong, Chrysler CEO Lee Iacocca held a low opinion of the M-body line as a relic of the pre-K car era and declined to invest any money in them. Despite lower gas prices in the mid- to late-1980s and a 2.26:1 rear-end gear ratio, the Diplomat's carbureted engine and lack of an overdrive gear on its TorqueFlite automatic transmission resulted in poor fuel economy compared with its larger competitors from Ford and General Motors, as evidenced by comparing the EPA estimates for 1986 models:
  Dodge Diplomat (5.2 L V8, 3-speed automatic): 16 city, 21 highway, 18 combined