car bucking

[289]

my 89 gt is not running right at no load situations. I cruise down the highway and under 2k it really bucks Like it is missing then its alright then missing again. Almost like the timing or the fuel mixture is changing under the same conditions. I had this problem before but it went away when I changed plugs and wires and put 89+ octane in it. I started puttin 87 in and it got really bad all of the sudden. Also I does not idle well any more up and down almost stalls then it catches its self What should I look for Thanks