You should be able to OBD2 swap if you want to go that route, but I'm not sure how possible tuning is with the current options besides what GTP091 mentioned. DHP can still be obtained, but support isn't what it used to be. redzmonte had a turbo 3.4 95 Monte that he swapped the OBD1.5 to OBD2 and tuned. I had tuned my 96 3.4 GP with DHP years ago. I believe you can run a 97 PCM and use HPT, who supports 97+ 3.4 Montes, so I'm not sure how that would work.
edit: after some research, looks like you can buy the DHP interface from the original manufacturer (AVT) and it SHOULD work. Setting up DHP on a Windows 10 laptop is a bit of a chore.
http://www.avt-hq.com/852_hw.htm
http://www.avt-hq.com/price.htm