Ever since I"ve owned my car (I currently have 101,000 miles) the transmission has shifted funny at times. Instead of seemless shifts like our 00 SSEi has with 42,000 miles, mine sort of slams itself into gears. It'* like it has a shift kit or something. The shifts are extremely quick and they give a tiny little jerk when shifting, it'* noticable, but it'* not enough to feel like a bad transmission exactly. It'* most noticable on the 2-3 shift, and also between 35 and 45 MPH while accelerating. When the Torque converter locks up, it feels like the transmission is "tugging" it is a very wierd sensation, I have never felt anyting like it. The RPMs will drop from around 2,000 RPM down to 1,000 RPM almost instantly and before it does this it will have a sort of shuddering while accelerating. (if you push the gas down a little when it'* in the 1,000 RPM range you can hear a growling sound coming from under the hood, it'* not the engine or anything like that. it'* wierd.) Like I said, it'* not bad enough to feel like a bad transmission, it just doesn't feel 'right.' also noticed under hard acceleration I can have seemless shifts like our 00 SSEi, but on low throttle applications is when it shifts rough. does that make any sense at all? You'd think it'd be the opposite, but it'* not. It has the smoothest shifts at around 3,000 RPM shifts, but if it shifts gears at around say, 1,800 RPm during acceleration it will shift hard.

had transmission flush at 98,000 miles, did not make much of a difference..

When im crusing at like 50 and my TC locks up mine will go down to 1.5 and sorta just sit there. No chugging sound. The engine just runs low and the car is staying consistent. Still quiet, you just hear exhaust change. It wont pop up till you give a fair ammount of gas then its fine. But if if i dont have it in overdrive its fine. Mine sometimes hard shifts in going from gas off to gas on in inner city traffic. But I dont think my tranny is going shes always sorta done it. I've had her for like 5k miles and she pulls hard. I think mine has to do more with computer than anything. I also have a different transmission.

Do you have Normal shift/Perform shift buttons??

I dont think the RIvera'* had them.

nope. :(
nope, no shif buttons. :(
I've also noticed that the 00 SSEi pulls a lot harder than mine at low throttle applications at low speeds even though we have the same gear ratios. once you've moving though say above 35 the riv will outrun the SSEi. but from 0 until around 35 the bonneville pulls smoother and stronger, it takes hardly any gas to get it moving, the riv takes a lot more gas, but I think it might just be the gas pedal on the bonneville has less travel on it so it feels like it takes less gas. I'm thinking the computers might be programmed differently because at the same acceleration level the bonneville shifts at 2,500 RPM and mine shifts at 2,000. (all shifts points are higher on the bonneville than my car. I'm guessing GM updated the chips on the later models to make driveability better. )