My trans has a bunch of clutch material on the dipstick and falls on its face HARD under wot when shifting from 3 to 5. I'm guessing it slips so badly that it is hitting rev limiter. I did install the go-go solenoid but it did not help my issue.

Since I bought the truck with 65k on it and it has a gooseneck, I'm guessing it was used to tow heavy heavy trailers, and the trans had seen better days anyways.

I'm considering sourcing a low mileage used 5r110 out of a wrecked truck. My other option is a Suncoast base level trans.

Please give me your opinions on either option.

 

I run my 6.4 on the 250 tune pull a lot and race a little here and there ive put 100000 miles on mine with this tune trans isn't as solid as the day I put it in but still fine I talked to the guys at spartan they said 300 files are good at takin a stock tranny out not a daily driver tune unless your really nice to it as far as a used tranny why bother id rebuild yours with sun coast or buy a sun coast tranny

 

Stock trans won't live long behind anything making 300 over stock . . . especially if you're pulling a trailer. You may be money ahead to build up the trans you have. Where are you located? I can work you a good deal on the parts you will need for the build. shoot me a PM and we can talk if your interested.