Since I've run my tunes, 87 perf and 87 economy, I experience a drive line bump when taking my foot off the accelerator. It doesn't do it all the time, but usually after reaching about 40 mph on a regular, no incline, acceleration it will bump. Feels similar to a bad u joint (checked them AOK) . I felt this bump even after 'softening up' the shift points to 25%. When I go back to stock it is nice and smooth.

Any ideas ?

 

Sounds kinda like a low throttle upshift. The programming is generally mapped out where the higher the throttle the lower the gear it needs to be in at a given speed. If you are in 3rd gear with 70% load and let off to 40% load, that may be in the 4th gear's area of the map. I'd contact the tuner and ask if there is anything going on in that area.

That's my hypothesis at least.

 

Sounds like your Torque Converter unlocking. It should unlock itself when you press the brake or let off the accelerator. Mine was doing it bad in 3rd and 4th. Got Mike at 5 Star to change my tune to keep the Torque Converter locked even when braking and deceleration that way when I get back on the gas it wont have to lock itself back up. Works like a charm now.

 

Thanks for the replies. Emailing VMP.

 

my truck does this and always wondered what it was, time to email somebody lol!

 

Any drawbacks to having your converter locked all the time? MPG? Smoothness? Wear and tear?

Thanks

 

I don't think it's locked all the time. If I understand it correctly it doesn't really lock up till you get up into 3rd and 4th gear. That's where my issues happened. I like to let off the throttle a lot to slow down and it was always causing it to unlock then re lock when I got back on it. Now when I'm up there it stays locked, much smoother riding. Seems to perform better overall now.