I have to correct myself on my jeep and what year it is, I have a 1990 not 91 jeep Laredo 4x4 with a transmission issue. I have checked fluids and I still can't get it to shift. I checked all the fuses and linkage. I am at a total loss now as to what the problem is. When I drive it it tacs out at 4000 rpm at 35 mph and will not up shift even manually. I have the 4.0 straight 6 and it's an automatic. Help