Torque Converter trouble on a 345

[Roquefort]

Hello!
We are german "Airstreamers", ,we bought a 345 classic in april and drove it cross country to the port and shipped to Germany. A wonderfull trip!
The rig is a 1986 classic 345 with 454cid engine and standard TH 475 (?) 3 speed tranny.
Before we left, The previous owner had it completely checked from Chevy truck service, with engine tune-up, oilchange in engine+tranny. Than the coach was checked from an Airstream dealer for eventuel neccessary repairs! (Adventure RV in Davenport/Quad Cities. I do not really recomand this shop anymore...! Many sefaults in repairs, not for a good rate, not very quick )
We have installed there also a Bank's Power System to improve gas mileage. Our baby was extremey well climbing hils, gas mileage also OK. With the "sweet spot" 65-70mls/h we got 10mpg.
Now we have a serious problem:
After we drove 1500mls cross USA and a few trips here in Germany, i had to realize some noise from underbelly with "bumbs" on the chassis.
I had to realize, 2 of 4 bolts from the transmission mount were gone, the 2 bolts in place were "handtight" only!
I fixed this, but i realized some lack of power, during accelaration. It became worse and worse, then we found unnormal noise, coming out of the torque converter, sounds like a metal fan is "scratching" the radiator?!
Coach is now barely drivable, very slow, impossible to travel anymore. I am afraid to use it more and more, do not want to "kill" the tranny!
Now my question: What is the torqueconverter i will need. The rig has much more torque with the Bank's system. I will add later also an Edelbrook performer kit for more torque (Intake manifold, camshaft, 750cfm carburetor).
We also tow a 6000 lbs trailer later, so we will need something VERY SOLID.
What do i need, what is the recomended "stall speed", where can i get this ?

[Waipio Rim]

If you were in the US, I would suggest swapping your transmission for a rebuilt unit. The guy we bought our 310 from cooked the trans by towing a trailer full of his household goods over the Rocky Mountains to Denver from California, and had it replaced fairly inexpensively. We do not tow, but the rebuilt unit has served us well for about 15,000 miles of travel including several trips over the Continental Divide, and is still as strong as when we got it. Shipping a trans to Europe might make working on what you have a better option, but that is beyond my ability.

[Smartstream]

The TH 400/475 is a very strong durable transmission. That being said it can be improved. Over on this side of the pond there are many knowledge technicians that rebuild the trans using stronger and better components from newer GM transmissions. The result is a better transmission. Mine was rebuilt this way more than 60000 miles ago and is still going strong. If you don't have technicians in Germany knowledgeable of these modifications I can get you a list of the parts used in my trans if you find a technician who wants to look at it. Also as you add towing weight you want to upsize you trans oil cooler to handle the extra heat generated.

Good luck.