Please help. 1994 Isuzu rodeo
 

Hello I need any help you guys can give. I have the 1994 isuzu rodeo 3.2 L v6 automatic transmission. I have recently encountered a strange problem. My accelerate had gone down but the weirdest thing is so driving surface streets it doesn't seem to have any problems other then acceleration. But when I get on the freeway it'll start good but after a little of driving at 60-75 MPH it'll start to decelerate or if I hit a hill or traffic then it won't easily get back up to speed. Because it'll shift into what's to be my knowledge as third gear then slowly bulid speed and rpms to 4500 rmps approximately 45 MPH then stop so I'll have to shift it to 4th by letting of the gas and slowly easing in it to get it to accelerate but if I give it to much it does what it should do and down shift to accelerate but it won't is almost as it hits a walk and actually slows down to the previously stated readings and last time the whole truck begin to hear above normal driving temp. So I added in an aftermarket trans cooler and replaced spark plugs and wires that imporoved driving slightly but I haven't taken it back out on the freeway because acceleration is still down and still feels when I hit higher speeds it doesn't want to so I was checking the trans wiring and the wires and plugs seem to be in pretty bad state I was going to originally just repair the wires tell I saw the plugs. So I was hoping someone in here knew where I could get a new wiring harness or how to fix the plugs or to see if anyone else can into that problem and knows a another fix for it or just any advice on what I have encountered anything would be greatly appreciated thank you.