'86 Trooper has no power

Me and buddy went half and half on an old 1986 Isuzu Trooper II. I had one before so I know the're reliable and good off-road. The motor runs storong and idles fine. The 4x4 works great. But when u hit the highway it has NO POWER. Or going up hills either. Sometimes it reaches 75mph down a hill, but it is extremely rare. the weird thing is, it did fine on the highway until I changed the oil and plugs. I checked and made sure I didn't screw up and put them in the wrong order also. Even had a mechanic friend check it out. I live in CO and hills are all over the place so being able to drive up them would be great. I'm going to change the gear fluid in the difs today and check the plugs also. Any suggestions or help on what to check next or replace or tune up would be greatly appreciated. Thanks!

Make sure that you put the plug wires back in the right spots..

I did, thanks

Check the distributer body and make sure it is secure. There is one bolt that holds it to the engine body and you loosen it up to set the timing. You might have got it out of position when replacing the wires. Check the timing , when engine is retarted it runs good but no power.

I suspect you are getting a weak spark. If your car had points they would be adjusted to close together. I'd check the coil, condensor, distributor cap. And the plugs. You used the right ones, right? You checked the gaps? Do you still have the old plugs. Put them back in and try them. If that solves the problem, buy another set of that brand plug.

Actually I did replace the plugs but the gap might be off. I made sure to get the right ones. I got Bosch truck plugs (I think the're Bosch). I also replaced the wires and got a little better in performance. Some Lucas oil aslo helped (exspecially with the difs). Thanks a lot for the info!

it's probably your catalitic converter

if you want to kill the performance of your vehicle continue using BOSH garbage if not stick some NGK's in it thats what it should have