I have a 99 F350 7.3 with an Automatic. 3.73 rear end and 35 inch tires. The Speedo has not been recalibrated and near as I can tell I am almost 10 off. I do a significant amount of driving in areas that have a 40 MPH speed limit and the local cops are brutal as to speeding tickets. so when I am showing 40 I am really going 44. Heres the question part. My Overdrive only kicks in above 40 so when I am driving around I have a hard time keeping it in OD. If I get the speedo recalibrated will that affect this or is the Overdrive and torque converter lock up independent of the speedo and based only on the pressures involved. I really personally don't care if I recalibrate or not, my only reason would be if it affects how the transmissions shifts. If I get the D-P chip will this change anything as to speeds that the overdrive is engaged. I asume that since I am just putt putting in these situations I am not damaging things by lugging the engine. If that is not true I want to know also. So far the only mod is AFE stage 2. Gauges are probably next then the tuner and exhaust.

I have been reading and really enjoy the information on this forum. when I figure out the signature I will set that up. Thanks!!

 

If you are doing a lot of driving at 40 or so turn off the OD IMO. IT shouldn't effect your milage and the tranny & Torque converter will thank you.