We are having the same "stuttering" problem with our 2001 Trooper. It's at around 90K and had all the transmission fluid changed at 70K. Took it to our mechanic and no codes came up, but when he drove it, he said it was the transmission. We took it to a transmission guy, and he too said no codes came up. Like a few others, our trooper seems to have shifting changes around 35-45 range... most notably. It feels as if it can't make up its mind about being in 3rd (?) or 4th (?) gear... quickly shifting up and down. About 3 weeks ago, right about 40 mph, the trooper started making a rather loud rumbling sound... brrrhhh that lasts until you let off the acceleration. The sound was rare... happened only 1 -2 times per week, but now will happen nearly every time you drive. Overall, the problem appears to be happening more frequently. When the shifting problem emerges, it tend to go away with firm acceleration or letting off the gas, and then resuming normally again. The problem is also most noticeable when tackling a grade or driving up a hill. Our transmission guy drove it, and didn't notice anything. So, I'm wondering whether or not replacing the electronic shift module or the solenoids is the best option. If the trans is bad, as in parts or broke or wearing beyond normal, will the trooper give a code? Any thoughts as to why there are no codes? Any input would be greatly appreciated. Thank you.