Natetf

i have a 4.0 1990 jeep wagoneer renix, that idles fine, and drives around town fine and when I take it over a pass to go down to Denver. But everytime I take it back over the pass, on the downhill side it idles fine, by whenever I hit the gas, it sputters and as soon as I pull over to look at it, it will have such a rough idle and sometimes die till it sits a few minutes and then I start it (if it dies) and it's fine the rest of the trip home. Distributor cap, spark plugs, and wires have all been changed. It is missing most of the emissions vacuum lines on the motor, but I'm replacing those this week. What else could maybe cause this issue??