so the back story to this one is that I had a th400 with a 3k B&M stall converter. It was a stock trans and unfortunately after a year the drum started and clutches started losing pressure and I picked up a th350 to replace it. I was told the th350 had clutches / shift kit / kolene steels but I have no proof of this other than it shifts firm and has no problem chirping the tires at full throttle. What i've noticed is the rpm difference between the 2 transmissions... I used the same 3k torque converter on the th350, and it revs 500rpm or so higher cruising than the th400 did. real number example.. 40mph on my th400 was 2000rpm, and now with the th350 its 2500rpm. is it because the drum is lighter on the th350? or that its too much stall for my setup now? did I get a lemon trans? or is it really my converter that's the problem? any insight would be amazing thanks, Jon

Transmission might be slipping. Clutch disks may be worn out or there's excessive clearance in the clutch pack. Converter stall depends on how much torque is put into it. It doesn't matter what's behind it.

Since your converter is rated at 3000 stall and you're cruising at 40 mph and 2500 rpm, the converter is still slipping because it hasn't reached it's stall speed yet. This slippage builds a lot of heat in the tranny oil.

theres an aftermarket cooler attached that I didnt mention earlier. the trans fluid doesnt look burnt or anything.

can the clutches slip that much and still shift hard?

I cant prove if this is in my mind or not but it just feels like theres some kind of resistance against the motor that wasnt there on the 400.

thanks for the info

Check your line pressures.