I have been dealing with the check engine light on my 94 trooper as well...it seems to come on when on the highway then off when i get off the highway...once it does come on my truck runs bad going up hills or when i give it gas.....does that sound familiar,? have you had any luck...so far I have
changed cat converter
changed EGR
cleaned injectors
changed fuel filter
cleaned maf sensor
changed o2 sensor
still hasent fixed the problem.....ill let you know if i fix it, please let me know how you make out