Okay, story time, I know it's long but I'm going to try to be accurate and forthcoming with any pertinent info I may have.

Truck in question is a 92 7.3l f350 2wd dually. My tach doesn't work under 1000 rpm and I've had harsh engagement if I'm not throttled down because of it for a few weeks, but it hasn't reached the top of my list, yet, mainly because I love the way sounds and it gives me an excuse. Tires were very bald and I got a great deal on a set so they topped the tach sensor. Had the tires put on another set of rims I had around and when I went to put them on one stubborn rim on the passenger's rear wouldn't budge, I torched, I pryed, I also had new rims so I beat, and it eventually let loose. Now in the process I did beat on the back side of the rim, quite hard you can decide if that's relevant later. So I cleaned up the rust and put on the new tires. No wobbles, that I notice no shakes. No lights when I start it, but after I pass maybe 10 mph I get a rear abs light and very soft engagement/ surges in rpm then comes back. I'm not great with auto Trans but it almost feels like it's driving in overdrive, and will surge to the correct gear then come back.

​​​​​I have looked and the only speed sensor I have is in the diff. I ohm checked the sensor and it comes back at a little over 1000 so I got one at O'Reilly that made no difference. So I tore open the pig, found gunk but no shavings, tone wheel in good shape, cleaned everything refilled with fluid and no change. I try to pull codes, but the light won't turn on until after I drive and I can't get it to give me codes by momentarily grounding after the light is on and truck running. I Unplugged the connector from the abs module and the sensor and put a jumper in place of the speed sensor and I get .6 ohms at the module. Plugged in the speed sensor and drive and get a smooth increase in current but not accurately. When I'm driving 0-10 I get no voltage, after that I get a smooth increase in voltage up to around 2.5 at 35mph.

Should I get the speed sensor direct from Ford or did I mess up the rear end. Or maybe more wiring issues. I'm nearly at the end of my rope with this auto Trans and am really close to just swapping it so these issues no longer arise. Any advice in any direction is appreciated.

 

You can swap the trans but it wont make the issue go away.You could install a high performance $5,000 E4OD reman,built to last behind a psd pulling truck but it would still act faulty with a bad tach sensor too.The trans needs to accurately read engine rpm or it can't shift correctly.