Is it a 1987 transmission? They still used a cable speedometer with an optical digital pulse generator in the gauges. If you have the DD sensor in the transmission going to the DD box I suspect the cruise output is being used as a VSS input for the 87 eco. You can change the pulse output from the DD so that may be something to try.
1941 Chevrolet AL 3/4 Ton previous Portsmouth Ohio Fire Dept
1959 Chevrolet 3100
1966 Chevrolet C10 "Sunoco Truck"
1986 Chevrolet C20 Crew Cab 454 lowered 6"
1991 Chevrolet R1500 Suburban LS 6.0/4l80e swap lowered on Qa1 coilers
1994 Chevrolet c1500 lowered 2/4 on 17x11 Billets
2000 Chevrolet Silverado 1500 full custom on air bags.
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