70 K10 engine stumbling ???

[tkeduk8r]

Well for the first time in nearly 10 years, old reliable isnt acting old relaible anymore... during the past few weeks, my 70 K10 350/sm465/NP205/3.73 is acting up... under load the engine will begin to stumble and even an occasional pop through the carb... the problem is not repetative in that it doent seem to follow a pattern as to when it happens, or the severity of it... the timing is set at 12 deg initial and i am running a pertronix ig module in stock dist. The carb is a holley (todd-68c15 or shawn-71swb4x4 would know) 4150? 600 cfm... this is the third diff tank of fuel and third diff station for fill up.. also the problem has been getting worse as time has gone on, starting with a minor miss (i thought arcing ignition wire) to now a 'might be bad for the motor if i keep driving" issue... any of you guys had similar problems??? thanks in advance...
--Mike