My 2005 Bonneville SLE just rolled over 132K and I'm getting the P1811 code along with a very, very, very long shift from 2nd to 3rd gear and leads to Engine KNOCK with multiple misfires, until I let off the gas and it will eventually shift into 3rd gear. If I drive like GRANNY the trans works fine, like intended, but if you give more than 1/2 pedal the problem also rears it'* ugly head, also when I'm on the highway and I kick it into passing gear it drops from 4th to 2nd and starts to surge, slip, misfire, and knock until I let off the gas, then it will shift into 3rd.

I heard that a simple 4T65-E Hard shift issue can be resolved with just a simple spring rebuild, found above the Trans filter will fix the P1811 error, I'm willing to try this for $43.71, the (1-2) (2-3) Shift Accumulators are known to break springs, and a simple kit "T84167G" found on Amazon , and a youtube video should point you in the right direction

I moved your post into its own thread. Please don't reply to other peoples threads with your own issues/problems. It just creates confusion etc. Thanks.

"T84167G" did the trick, it feels like I have a new transmission, should have done this years ago..