L7 doesn’t disable DFM??

schindles · July 5, 2022

Purchased ‘22 LTD with 5.3L 8-speed w/DFM on 3/28. When driving in “D”experienced weird up/down shifting in gears 1-3 along with some shuttering that people have reported here. Read a ton on DFM horror stories so I’ve been driving in L7 for the last 4K miles. Shifting improved, but it was still “clunky”. Installed a Pulsar LT over the weekend and man what a difference. Tranny shifts feel buttery smooth now and I’ve lost 1-2 mpg since then. This leads me to believe that driving in L7 does nothing in terms of disabling DFM. Has anyone else experienced this? Or can anyone confirm definitively if L7 does disable DFM?

mafd2 · July 6, 2022

What's the build date on your LTD? Are you sure you have DFM? My '22 refresh doesn't have DFM and boy am I glad.

schindles · July 10, 2022

Yes, I'm sure. It's on my window sticker with the engine. I'm not entirely sure on my build date. I went to some website that was posted here were you could email GM directly and give them your VIN and they would tell you the exact build date. I received a response the next day saying that GM won't give out that information anymore (likely due to all of the DFM issues people have had in that affected date range).

voided3 · July 11, 2022

I can tell L7 disables DFM on our '21 Silverado 5.3 with the 8-speed, especially at low speeds, and I always drive in L7 unless I need to go 75 MPH or faster (which is rare around around here; our local highways only go up to 65 MPH speed limits). With that said, the shifts can still be clunky often due to the shift programming and probably other physical design factors of the 8L90 transmission, but I can tell by watching the tachometer that it isn't locking and unlocking the torque converter nearly as much in L7 as with DFM enabled in D.

I've adapted my driving style to avoid the clunks, including holding it in neutral shifting between reverse and drive for at least two seconds, but inevitably it'll still act clunky when letting off the throttle to coast or sometimes when coming to a complete stop, for example. It almost feels like a faulty motor mount or loose torque converter bolts, but unless it throws a code or can't move under its own power, I know it'll be a "cannot duplicate" or "operating as designed" diagnosis at the dealer. It's not GM's finest work, that's for sure.

Edited July 11, 2022 by voided3

schindles · July 12, 2022

Yikes! Well thanks for your reply. I'm glad to know that it can still be disabled by L7. However, if that has been your driving experience thus far, then I would highly recommend putting a Pulsar on your truck. That's crazy that the transmission would still act that way in L7. My Pulsar has really helped with the shifting of my truck then in that regard. It's (almost) enjoyable now with only the occasional "weirdness". My only concern is when I have to bring it back to the dealer for some warranty work and for installing the heated seat chips. I'm not looking forward to taking it off and having to re-install it afterwards.

voided3 · July 12, 2022

1 hour ago, schindles said:

Yikes! Well thanks for your reply. I'm glad to know that it can still be disabled by L7. However, if that has been your driving experience thus far, then I would highly recommend putting a Pulsar on your truck. That's crazy that the transmission would still act that way in L7. My Pulsar has really helped with the shifting of my truck then in that regard. It's (almost) enjoyable now with only the occasional "weirdness". My only concern is when I have to bring it back to the dealer for some warranty work and for installing the heated seat chips. I'm not looking forward to taking it off and having to re-install it afterwards.

Yeah, that's what has kept me from doing anything that could be considered a modification on our truck. We had lifter failure on ours at 585 miles and got an extended component coverage letter for the engine and related components, after the back and forth hassle of getting that addressed over a few months, so I decided to stick with the "L7 method".

The other factor is we'd like to replace the truck with a gas 3/4 ton within the next year (if possible, given the current market) as A) we may upsize our travel trailer, B) the GM and Ford HD trucks don't have cylinder deactivation, and C) I've been really unimpressed with the build quality/ownership experience on this particular truck (the lifters weren't the only issue) and I feel keeping it past the warranty period would be a bad financial move.