Stumbly....I searched already

OK, my 96 is running rough, and I can't figure it out. I'd rather not pay to have it done.

It idles fine, runs OK when cold, stumbles, especially on acceleration, to the point of not being able to get up to highway speeds. It started this last night after about 20 miles dirt, five low range, and a couple shallow water crossings. I let is sit overnight, checked conenctions on cooling relay and the O2 sensor (front) I did a few weeks ago, and it still does it once warmed up.

I have a check engine light, trouble codes. 35 and 15 (followed by a single 6?)

So, 35 is a cooling relay open or shorted or a idle switch motor fault. The auxilary cooling fan comes on and off fine, temp runs about right. It 'idles' fine. Do these mean anything for what I'm doing?

15 is 'no speed sensor distance sensor signal'. What the $%^ is that? Cruise control works fine.

It's a 96 with 170k, 4.0, recent O2 sensor and bottle of injector cleaner. It did this stumble once right after the O2 sensor, but I figured it was just crud that the cleaner broke loose. Now it's worse and persistent.

Thoughts?

I think I would read the codes with a reader, there are no signal number codes.

I thought the key-blink-blink trick worked with a 96?

It seemed to when I did the O2 sensor (or maybe just unplugging the battery and resetting it hid whatever problem was orginally there?)

Do I need to take it to the shop? I'd rather not, but I need something relatively reliable to get to work.

Help please guys!