09 f250

I bought a 09 f250 that has a Diesel conversion specialists 12 valve swap I tore it all apart to redo the frame and paint under the cab got it all back together and I cannot get the tack to work and I'm assuming that's why it wants to start off in 2nd or 3rd gear the transmission just feels like it's trying to start in 3rd or in between gears if that's even possible it goes in reverse just fine or maybe it has something to do with the trans range sensor also wondering where the 6.4 gets it's rpm reading any help would b greatly appreciated

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There's two options for the tach on these swaps. Check around your harmonic balancer for a pickup sensor and trace the wiring back. If there is no sensor there then it's in the back of the block picking up off of the back of the cam. Hopefully you have the swap helper tach sensor but it doesn't sound that way