Very severe jerking accelerating mid-range

[SVXIoM]

I have a bucking bronco problem on my '96 UK model with 120,000 miles. From starting I have a slightly lumpy tickover and slight hesitations when accelerating but when the engine has been running for 1-1½ hrs acceleration in D between 1500 and 2500 rpm starting from the cruise produces violent jolting/mis-firing only stopped by dropping into 3 whence no problem. 3000rpm upwards in D produces no problem and is smoothest part of the range. No hi-revs mis-firing in any gear. Just replaced TPS and cleaned MAS but problem not gone away albeit smoother gear changes. No access to scanner here so may have to go to UK to find suitable scanner (what type suitable?). Any suggestions in priority order would be most welcome.