I live in the mountains and have 2006 GM that down shifts when hill climbing and then immediately upshifts. The tach sort of bounces between 1200 to 2000 and back to 1200 RPM.

I also have a 2009 GM and when it down shifts it stays around 2000 RPM and drives smooth. The 2009 gives me a comparison point about how these cars are supposed to drive.

I would appreciate troubleshooting ideas for my 2006 GM, most likely transmission.

In stock trim these transmissions hunt for which gear to be in excessively. Especially 3-4.

Since I jmodded my transmission and installed the Sonnax overdrive pin kit with the included washer that firms up overdrive the transmission shifts beautifully and it no longer hunts or seems unsure of which gear to be in.

My 2009 doesn't do the same and is stock. Did they change the design between 2006 and 2009?

I believe each year they made improvements on the transmissions.

I drive some pretty extreme roads in terms of steepness. Bet the Ford engineers never anticipated such roads working out of Michigan. Any car manufacturer would dramatically improve their product for Cali if they drove their prototypes up the Grapevine AKA the car eating hill when is 110 degrees with the AC blasted and at full capacity.

Sounds like your recommended MOD would make my 2006 shift more like my 2009. The comparison with the 2009 may be shining a light on what you call hunting?

https://www.idmsvcs.com/2vmod/tranny/modelnumbers/crownvic/index.html


List year by year of updates

I had a 2011 that did the same thing. In hilly country with ups and downs it would “search” for the right gear, upshifting and downshifting, sometimes many times in a short space of road and usually between 40 and 50 mph. sometimes it would do it at lower speeds and a little more erratically but in hilly ups and downs at those speeds it could be guaranteed to do It.

I feared a full transmission swap or rebuild was going to be necessary but I had a friend who told me that the electronic sensor was probably occluded by dirty or cloudy Transmission fluid. He recommended a full fluid swap with changing the filter as well. He then said just drive it a while after the swap.

I had a Ford dealer do the work about $300 after completion they drove it a little bit and said the problem is still there, but within 100 miles of driving it completely went away and I never had another shifting miss of 3000 miles of driving before I sold it.

Coincidence or causality? I don’t know but it sure seem to work.

I just changed the filter and all the fluid about 1,000 miles ago.

These might be the words that explain the difference between my 2006 and 2009. "Also, the transmission fluid was changed to Mercon LV (part number XT-10-QLV) and the valve body updated."

You reworked your valve body, which probably made it closer to the 2009.