I am familiar with both the 6L80 and 6L90 transmissions.
Between the two, there's an important difference in so-called manual shifting.
For both transmissions, M1 gives you a 1 speed transmission; M2 gives you a 2 speed transmission, M3 gives you a 3 speed transmission, and so on up to M6.
With the 6L90, with "D" selected, regardless of what gear the transmission is in at the moment you select manual mode "M", the current gear is preserved. If the transmission was in 3rd gear when you selected manual mode "M", the transmission would remain in 3rd gear (unless you tried to over-rev the engine in which case the transmission would upshift to prevent damage). The same gear behavior applies regardless of the gear the transmission was in when you selected "M".
But, incredibly, with the 6L80, selecting "M" (which ironically stands for "manual") will cause an automatic downshift of one gear* if the transmission was in 3rd, 4th, 5th, or two gears if the transmission was in 6th.
I am familiar with both the 6L80 and 6L90 transmissions.
Between the two, there's an important difference in so-called manual shifting.
For both transmissions, M1 gives you a 1 speed transmission; M2 gives you a 2 speed transmission, M3 gives you a 3 speed transmission, and so on up to M6.
With the 6L90, with "D" selected, regardless of what gear the transmission is in at the moment you select manual mode "M", the current gear is preserved. If the transmission was in 3rd gear when you selected manual mode "M", the transmission would remain in 3rd gear (unless you tried to over-rev the engine in which case the transmission would upshift to prevent damage). The same gear behavior applies regardless of the gear the transmission was in when you selected "M".
But, incredibly, with the 6L80, selecting "M" (which ironically stands for "manual") will cause an automatic downshift of one gear* if the transmission was in 3rd, 4th, 5th, or two gears if the transmission was in 6th.
WTF??
- Michael M., Utica, MI, US