torque converter lock-up

Hi Folks . First time poster. I have a '94 Dodge caravan with a 3 speed lock-up tranny.The vehicle has been virtually trouble free. It has 183k(112k miles) and is starting to blow blue=rings,seals? But that is another problem. My question is:
Is there a way to set the factory setting of the lock-up of the torque converter to lock-up at a higher speed . I have always been annoyed at the low 66kmh(41mph) speed of the lock-up. I equate the performance and responsivness to like, driving a standard transmission and being in too high of a gear when going up a grade.
I have been lucky with this tranny and have only had one relatively minor problem at the 70K(kms) mark. A pin broke that allowed me to only reverse at idle . Any throttle would result in heavy vibration. Luckily this was a $180.00 job fixed under warranty. I have had regular tranny fluid and filter changes at the 40k(kms) intervals since I bought it new..
I now am having the tranny vibrate and shake the vehicle when the tranny goes into lock-up at it's lowest speed of 66 kmh. At highway speeds it is not noticable.I may disconnect the plug that engages the lock-up to help the tranny as I do mostly city driving. I have done this( disconnect the plug to converter) to my inlaws 91 Pontiac 6000 who had a similar problem and it runs fine for the last year and a half.
Any one got help on this one?

I am unsure if what I say applies to a Caravan, so take what I have to say with a grain of salt.

I worked on a 92 Spirit with the 3-speed transmission with a problem that seems to be the reverse of yours. You seem to want the shift speeds to delay and stay in a lower gear. The problem I saw was that the transmission would upshift and downshift at higher speeds than normal (3'rd gear at 46mph instead of 35). The car would drive mostly in second gear around town, but on the highway it was ok. The problem in this case turned out to be a transmission cable had fallen off the gas pedal.

See if your Caravan's has a cable connecting from the 3-speed transmission and going to your gas pedal. This is a different cable than the one going to your motor's accellerator. That cable is used by the 3 speed transmission as a vehicle speed indicator. In the old days with carbertors, there was linkage to the transmission to cause downshifting on hitting the gas. This cable also has something to do with the modern day equivilent of that.

It sounds like you want to adjust that cable, but I don't believe it is possible. If you disconnect that cable from the accelerator pedal, the up/down shift points occur at higher rpms, The PCM will also set a code 37, but the CES light will not go on. The code 37 just means that the PCM has detected that the transmission is not shifting at the preprogrammed speeds.