i have a 94 pickup 3.0 4wd automatic.. I know I've heard that the cross over will not work and I'll have to get an ecu and depending the motor I may or may not have to change oil pans and dip stick. But I know for a fact I'm missing something it just sounds a little to simple. I'm also getting the ors harness. Can anyone tell me what I'm missing?

 

It really depends on what the donor is and how much of the 3.4 you're getting. When you go looking for it, try to get the ECU that came with the motor, the wiring harness and all plugs for same, all the VSVs and EVAP box. Air cleaner box is a plus, but not a deal breaker by any means. The power steering pump, and alternator are different, so try to get those if at all possible. You can reuse your AC compressor, but you need to change your pulley from a v-belt type to a grooved belt type. If you can get the 3.4 drive plate or flywheel (depending on transmission type), this will save you a little bit of hassle down the road, but you can reuse the 3.0 parts if necessary. Whichever way you go, use the starter for the flywheel you use.
In general, an older engine is more desirable. Fewer things are different between a 3.0 and a 96 or 97 3.4 than between the 3.0 and an early 2000s engine. Less changes = less headaches to make it work.

 

Like gryphonrunner said, get as much as you can from the donor vehicle as possible. Brackets, p/s pump, alternator, ECU, engine harness, a/c compressor, vsv's, vapor canister, anything attached to the motor. Some of it may not get used, but if you need it, you'll have it. If you plan on keeping your original transmission, try to find a t100 4wd auto for your donor and get the ECU. And if possible, grab the neutral safety switch off the donor tranny. That will save you some money in the end when you're getting it all hooked up. If you are swapping in a manual or are going to use a later model auto, then those pieces aren't as critical and can be dealt with in the conversion harness. Keep researching. Understand as much as possible about your swap before you start. Contact ORS early on if you're going to use them for your conversion harness. They are a wealth of information and were always willing to help when I did mine.